Part 2
. Birds. J. Anim. Ecol. 5:370-389.
Heath, H. 1915. Birds observed on Forrester Island, Alaska, during the summer of 1913. Condor 17:20-41.
Hubbs, C. L., A. L. Kelly, and C. Limbaugh. 1970. Diversity in feeding by Brandt's cormorant near San Diego. Calif. Fish Game 53:156-165.
Idyll, C. P. 1973. The anchovy crisis. Sci. Am. 228:22-29.
Imber, M. J. 1973. The food of grey-faced petrels (_Pterodroma macroptera gouldi_ Hutton), with special reference to diurnal migration of their prey. J. Anim. Ecol. 42:645-662.
Ingolfsson, A. 1967. The feeding ecology of five species of large gulls _(Larus)_ in Iceland. Ph.D. Thesis. Univ. of Michigan, Ann Arbor. 186 pp.
Jewett, S. G., W. P. Taylor, W. T. Shaw, and J. W. Aldrich. 1953. Birds of Washington State. Univ. of Washington Press, Seattle. 767 pp.
Koelink, A. F. 1972. Bioenergetics of growth in the pigeon guillemot, _Cepphus columba_. M. S. Thesis. Univ. of British Columbia, Vancouver, Canada. 71 pp.
Komaki, Y. 1967. On the surface swarming of euphausiid crustaceans. Pac. Sci. 21:433-448.
Kooyman, G. L. 1974. Behaviour and physiology of diving. Pages 115-138 _in_ B. Stonehouse, ed. The biology of penguins. Macmillan, London.
Kortright, F. H. 1942. The ducks, geese and swans of North America. Wildlife Management Institute, Washington, D.C., and Stackpole Co., Harrisburg, Pennsylvania. 476 pp.
Kozlova, E. V. 1961. Fauna of the U.S.S.R., Birds: Alcae. (Transl. from Russian.) Israel Program for Scientific Translations, Jerusalem. 140 pp.
Kuroda, N. 1954. On the classification and phylogeny of the order Tubinares, particularly the shearwaters _(Puffinus)_. Herald Co., Tokyo. 179 pp.
Kuroda, N. 1955. Observations on pelagic birds of the Northwest Pacific. Condor 57:290-300.
Laws, R. M. 1977. The significance of vertebrates in the Antarctic marine ecosystem. Pages 411-438 _in_ G. A. Llano, ed. Adaptations in Antarctic ecosystems. Gulf Publishing Co., Houston, Texas.
Linton, C. B. 1908. Notes from Santa Cruz Island. Condor 10:124.
Mabbot, D.C. 1920. Food habits of seven species of American shoal-water ducks. U.S. Dep. Agric., Bull. 862. 68 pp.
Madsen, F. J. 1957. On the food habits of some fish-eating birds in Denmark. Dan. Rev. Game Biol. 3(2):19-83.
Manuwal, D. A. 1974. The natural history of Cassin's auklet _(Ptychoramphus aleuticus)_. Condor 76:421-431.
Martin, P. W. 1942. Notes on some pelagic birds off the coast of British Columbia. Condor 44:27-29.
Martin, P. W., and M. T. Myers. 1969. Observations on the distribution and migration of some seabirds off the outer coasts of British Columbia and Washington State, 1946-1949. Syesis 2:241-256.
McGilvrey, E. B. 1967. Food habits of sea ducks from the northeastern United States. Pages 142-145 _in_ Wildfowl Trust 18th annual report.
Miller, L. 1936. Some maritime birds observed off San Diego, California. Condor 38:9-16.
Miller, L. 1940. Observations on the black-footed albatross. Condor 42:229-238.
Munro, J. A. 1941. Studies of waterfowl in British Columbia: the grebes. B. C. Prov. Mus. Occas. Pap. 3. 71 pp.
Munro, J. A., and W. A. Clemens. 1931. Waterfowl in relation to the spawning of herring in British Columbia. Biol. Board Can. Bull. 17. 46 pp.
Munro, J. A., and W. A. Clemens. 1939. The food and feeding habits of the red-breasted merganser in British Columbia. J. Wildl. Manage. 3:46-53.
Murphy, R. C. 1936. Oceanic birds of South America, Vol. 2. Macmillan, N. Y. 604 pp.
Ogi, H., and T. Tsujita. 1973. Preliminary examination of stomach contents of murres (_Uria_ spp.) from the eastern Bering Sea and Bristol Bay, June-August, 1970 and 1971. Jpn. J. Ecol. 23:201-209.
Oliver, W. R. B. 1955. New Zealand birds, 2nd ed. A. H. and A. W. Reed, Wellington, New Zealand.
Pacific Seabird Group. 1975. Policy statement: Incidental seabird kills from salmon gillnet fisheries. Pac. Seabird Group Bull. 2:19-20.
Palmer, R. S. 1962. Handbook of North American birds. Vol. 1. Yale Univ. Press, New Haven, Connecticut.
Pearson, T. H. 1968. The feeding biology of sea bird species breeding on the Farne Islands, Northumberland. J. Anim. Ecol. 37:521-551.
Perthon, P. 1968. Food and feeding habits of the common eider _(Somateria mollissima)_. Nytt. Mag. Zool. 15:97-111.
Phillips, R. E., and G. D. Carter. 1957. Winter food of western grebes. Murrelet 38:5-6.
Preble, E. A., and W. L. McAtee. 1923. A biological survey of the Pribilof Islands, Alaska. U.S. Bur. Biol. Surv. N. Am. Fauna 46. 255 pp.
Richardson, F. 1961. Breeding biology of the rhinoceros auklet on Protection Island, Washington. Condor 63:456-473.
Ripley, S. D. 1975. The view from the castle. Smithsonian 6:6.
Robbins, C. S., B. Brunn, and H. S. Zim. 1966. Birds of North America. Golden Press, N. Y. 340 pp.
Roberts, A. A., and E. H. Huntington. 1959. Food habits of the merganser in New Mexico. N. M. Dep. Fish Game, Bull. 9. 36 pp.
Robertson, I. 1974. The food of nesting double-crested and pelagic cormorants at Mandarte Island, British Columbia, with notes on feeding ecology. Condor 76:346-348.
Robertson, I. 1972. Studies on fish-eating birds and their influence on stocks of the Pacific herring, _Clupea harengus_, in the Gulf Islands of British Columbia. Herring Investigations, Pac. Biol. Stn., Naimo, B.C. 28 pp. (Unpublished report)
Sanger, G. A. 1972. Preliminary standing stock and biomass estimates of seabirds in the subarctic Pacific region. Pages 589-611 _in_ A. Y. Takenouti et al., eds. Biological oceanography of the northern north Pacific Ocean. Idemitsu Shoten, Tokyo. 626 pp.
Sanger, G. A. 1973. Pelagic records of glaucous-winged and herring gulls in the north Pacific Ocean. Auk 90:384-393.
Sanger, G. A. 1974. A preliminary look at marine mammal food-chain relationships in Alaskan waters. U.S. Natl. Mar. Fish. Serv., Mar. Mammal Div., Seattle. 29 pp. (Unpublished report)
Schaefer, M. S. 1970. Men, birds and anchovies in the Peru current--dynamic interactions. Trans. Am. Fish. Soc. 99:461-467.
Scott, J. M. 1973. Resource allocation in four synoptic species of marine diving birds. Ph.D. Thesis. Oregon State Univ., Corvallis. 97 pp.
Scott, J. M., J. Butler, W. G. Pearcy, and G. A. Bertrand. 1971. Occurrence of the Xantus' murrelet off the Oregon coast. Condor 73:254.
Sealy, S. G. 1972. Adaptive differences in breeding biology in the marine bird family Alcidae. Ph.D. Thesis. Univ. of Michigan, Ann Arbor. 283 pp.
Sealy, S. G. 1973_a_. Interspecific feeding assemblages of marine birds off British Columbia. Auk 90:796-802.
Sealy, S. G. 1973_b_. Breeding biology of the horned puffin on St. Lawrence Island, Bering Sea, with zoogeographical notes on the North Pacific puffins. Pac. Sci. 27:99-119.
Sealy, S. G. 1975. Feeding ecology of the ancient and marbled murrelets near Langara Island, British Columbia. Can. J. Zool. 53:418-433.
Serventy, D. L., V. Serventy, and J. Warham. 1971. The handbook of Australian sea birds. A. H. and A. W. Reed, Wellington, New Zealand. 254 pp.
Sheard, K. 1953. Taxonomy, distribution and development of the Euphausiacea (Crustacea). Rep. B.A.N.Z. Antarct. Res. Exped., Ser. B (Zoology and Botany), 8:1-72.
Shuntov, V. P. 1972. Sea birds and the biological structure of the ocean. (Transl. from Russian.) Bur. Sport Fish. Wildl. and Natl. Sci. Found., Washington, D.C. Nat. Tech. Inf. Serv. TT 7455032. 566 pp.
Smail, J., D. G. Ainley, and H. Strong. 1972. Notes on birds killed in the 1971 San Francisco oil spill. Calif. Birds 3:25-32.
Spaans, A. L. 1971. On the feeding ecology of the herring gull _Larus argentatus_ Pont. in the northern part of the Netherlands. Ardea 59:73-188.
Spring, L. 1971. A comparison of functional and morphological adaptations in the common murre _(Uria aalge)_ and thick-billed murre _(Uria lomvia)_. Condor 73:1-27.
Stejneger, L. 1885. Results of ornithological explorations in the Commander Islands and Kamchatka. U.S. Natl. Mus. Bull. 29:7-362.
Sverdrup, H. V., M. W. Johnson, and R. H. Fleming. 1942. The oceans: their physics, chemistry and general biology. Prentice-Hall, Englewood Cliffs, N. J. 1087 pp.
Swartz, L. G. 1966. Sea-cliff birds. Pages 611-678 _in_ N. J. Wilimovsky and J. N. Wolfe, eds. Environment of the Cape Thompson region, Alaska. U.S. Atomic Energy Commission, Div. Tech. Inf., Oak Ridge, Tennessee. 1250 pp.
Thoresen, A. C., and E. S. Booth. 1958. Breeding activities of the pigeon guillemot, _Cepphus columba columba_ (Pallas). Dep. Biol. Sci., Walla Walla College, Washington, Publ. 23. 34 pp.
Tuck, L. M., and H. J. Squires. 1955. Food and feeding habits of Brunnich's murre _(Uria lomvia lomvia)_ on Akpatok Island. J. Fish. Res. Board Can. 12:781-792.
Uspenski, S. M. 1958. The bird bazaars of Novaya Zemlya. (Transl. from Russian.) Transl. by Department of Northern Affairs and Natural Resources, Canada. 159 pp.
Ward, J. G. 1973. Reproductive success, food supply, and the evolution of clutch-size in the glaucous-winged gull. Ph.D. Thesis. Univ. of British Columbia, Vancouver, Canada. 119 pp.
Wetmore, A. 1924. Food and economic relations of North American grebes. U.S. Dep. Agric., Bull. 1196. 23 pp.
White, C. M., W. B. Emison, and F. S. L. Williamson. 1971. Dynamics of raptor predation on Amchitka Island, Alaska. Bioscience 21:623-627.
White, C. M., W. B. Emison, and F. S. L. Williamson. 1973. DDE in a resident Aleutian Island peregrine population. Condor 75:306-311.
Zelikman, E. A. 1961. The behavior pattern of the Barents Sea Euphausiacea and possible causes of seasonal vertical migrations. Int. Rev. Ges. Hydrobiol. Hydrogr. 46:276-281.
FOOTNOTES:
[15] Present address: U.S. Fish and Wildlife Service, Office of Biological Services, 1011 East Tudor Road, Anchorage, Alaska 99503.
[16] Other incidental prey were squid and atherinid fishes, both at the Farallon Islands.
[17] Other incidental prey were squid and such fishes as atherinids, _Zaniolepis_, _Genyonemus_ and _Peprilus_ at the Farallones, and atherinids, _Trachurus_ and _Heterostichus_ at San Diego.
[18] Other incidental prey were polychaetes at Netarts and the Farallon Islands.
[19] Principal sources: Bent 1925; Cleaver and Franett 1945; Cottam 1939; Cottam and Knappen 1939; Kortright 1942; Mabbot 1920; McGilvrey 1967; Munro and Clemens 1939; Roberts and Huntington 1959.
[20] Other incidental items were the fish _Cololabis_ and _Peprilus_ at the Farallon Islands.
[21] Other incidental items were myctophid fish in northeastern Canada.
[22] Other incidental items included the lamprey _(Lampetra)_ at the Farallon Islands.
[23] Bent (1946) listed "fish" as prey.
[24] Grinnell (1897) listed "fish" as the major dietary component.
[25] Bédard (1969_a_) also listed "fish" as an incidental item.
[26] Other incidental prey were copepods and isopods.
[27] Other incidental prey were pholids in Denmark.
[28] Other incidental prey were copepods and cephalopods in North Atlantic areas.
[29] Other incidental prey were isopods in western North America and fish eggs near Vancouver Island.
[30] Other incidental prey were fish eggs in Denmark.
[31] Offal from wounded whales and seals, and bits of food, primarily crustaceans and fish, from feeding whales are important scavenger foods (Bent 1922).
[32] Other incidental prey were isopods in the North Pacific.
[33] Other incidental prey were the fish _Merluccius_ at the Farallon Islands.
[34] Other incidental prey were isopods near the Pribilofs and in the Chukchi Sea, and amphipods in the latter area; Bent (1921) considered "crustaceans" to be major prey.
[35] Study conducted during period of breeding failure.
[36] These are the "food categories" of Tables 11-15. Items included in diets are not included here.
[37] Proportion based on the arbitrary assumption that half (5) of the 11 species in question catch and eat birds at sea.
[38] Information on body sizes (length) is from Robbins et al. (1966).
[39] Information on bill lengths is from Palmer (1962), Dement'ev et al. (1968), and Friedmann (1950).
[40] Feeding methods are from Ashmole (1971) as adapted by Ainley (unpubl. manuscr.).
Population Dynamics in Northern Marine Birds
by
William H. Drury
College of the Atlantic Bar Harbor, Maine 04609
Abstract
It seems only reasonable to assume that populations of marine birds fluctuate even when not disturbed by man; such fluctuations would result both from the secondary effects of species adaptive tactics and from changes in the marine environment. I briefly review some human activities and some other natural processes that have resulted in changes in numbers and distribution of seabirds and present a short discussion of theoretical models which emphasizes that conclusions drawn or predictions made from models of the dynamics of populations depend upon the assumptions about stability that were used in preparing the models. I then review those special characteristics of seabirds which are directly relevant to planning programs intended to protect seabirds or encourage their increase and identify several goals for improving our understanding of the population dynamics and biology of marine birds. My general conclusion is that enough is already known to undertake effective conservation programs, and that time is pressing.
Seabirds have been categorized as renewable resources in only a few places, although their symbolic value has been recognized for centuries (for example, the medieval poem "The Seafarer" and the designs on Saint Cuthbert's tunic). With the exception of the Russians (Belopol'skii 1961; Uspenski 1956), the Australians (Serventy 1967), and the Icelanders, industrialized peoples have not considered seabirds to be salable and therefore worth managing. Yet during many centuries the seabirds of the northern seas were a major food for coastal and island villages (Bent 1919, 1921, 1922; Fisher and Lockley 1954).
Some biological principles that affect the dynamics of seabird populations are identified in this paper. I believe these principles must form the basis of plans to maintain and increase seabird numbers.
I describe some observations of population changes, review briefly the conflicting theoretical frameworks for population dynamics, and identify some of the biological characteristics of marine birds that affect the way in which population changes occur. The terms "seabirds" and "marine birds" are used interchangeably for those bird species which depend upon salt water for some part of their annual cycle (c.f., the Pacific Seabird Group).
Population Fluctuations
Broadly stated, the populations of northern seabirds have shown marked short-and long-term fluctuations. Most authors have assumed that all such fluctuations reflect human disturbance of the natural system, because of the obvious effects of human predation during the last 200 years.
_Human Impact_
In the centuries before people traveled extensively between islands, seabirds were taken in ways that we judge must have allowed the survival of the colonies (e.g., those at the Faroes or Saint Kilda, those in Iceland and Greenland, or those in the Aleutian Islands and the Bering Strait). We presume either that the populations of island peoples were regulated by shortage of resources other than seabirds or that those who overcropped and eliminated the seabirds suffered the consequences.
Negative Effects
When a sea-going, commodity-oriented way of life evolved, seabirds were killed in huge numbers for such uses as the plumage trade, fish bait, or rendering into oil (Tuck 1960; Fisher and Lockley 1954). Even the elimination of several colonies--e.g., Funk Island, Newfoundland (Tuck 1960); Seal Island, Eastern Egg Rock, Maine (Norton 1921); Muskeget, Massachusetts (Forbush 1929)--may have had little effect on the rate of cropping because those who killed off one source could probably seek out another. As the colonial seabirds became scarce they became more valuable, which stimulated more intensive pursuit of the remnants (Dutcher 1901, 1904).
In some places where seabird colonies did not supply a croppable economic resource, the islands were used for alternative crops with at least temporary commodity value (e.g., foxes were introduced in the Aleutian Islands; Bent 1919). Large herbivores were introduced to supply meat for island residents (e.g., Saint Matthew Island; Klein 1959), as well as pigs, cattle, sheep, goats, and rabbits on islands in the North Atlantic and southern oceans (many authors). Increases in many seabird populations over the last 75 years have been generally associated with relief from predation by humans such as the fowlers, eggers, and plume hunters of the 19th century. Such relief may have been partly responsible for the increase of North Atlantic gannets, _Sula bassana_, and common murres or guillemots, _Uria aalge_ (Fisher and Vevers 1943, 1944; Cramp et al. 1974). On a smaller scale, several population increases along the coast of New England have been recorded following the enactment of protective legislation (Dutcher 1901, 1904; Norton 1921, 1924; Palmer 1949; Drury 1973).
Coulson (1974) argued that in addition to relief from predation, the explosion of the population of kittiwakes _(Rissa tridactyla)_ in this century resulted from access to previously un-occupiable breeding sites. Nesting cliffs and buildings suitable for kittiwake nesting are abundant and now protected from egging or fowling.
Positive Effects
There can be little doubt that human activities have also had marked positive effects in some cases. For example, Fisher (1952) suggested that the North Atlantic fulmar _(Fulmarus glacialis)_ was provided food first by whaling, then by commercial fishing, and that this food allowed the species to increase steadily over the last 3 centuries.
The worldwide increase of gulls (_Larus argentatus_, _L. fuscus_, _L. dominicanus_, _L. ridibundus_, _L. novae-hollandii_) has been credited to availability of food from wasteful human garbage disposal (Murray and Carrick 1964; Fordham 1968, 1970; Harris 1964; Harris and Plumb 1965; Kadlec and Drury 1968; Brown 1967; Mills 1973; Vermeer 1963).
It is hard to dismiss the evidence pointing to the impact of human
## activities on seabird populations during the last 3 centuries. Yet
it would be misleading to assume that without man's interference seabird populations would have remained stable. Success in designing programs of protection and population enhancement must allow for the realities--that seabird populations fluctuate inherently, and that secular changes occur regularly in their environment.
_Impact of Natural Events_
Some population changes appear to result from sudden impacts; other changes are gradual.
Sudden Disasters
Gromme (1927) reported windrows of dead murres in the Unimak Pass and Alaska Peninsula; die-offs of murres in winter storms in the Atlantic and Arctic Oceans were reported by Tuck (1960) and Dement'ev et al. (1968).
Recently some mass mortalities have been associated with specific causes. Bailey and Davenport (1972) reported that starvation caused the die-off of common murres in the southern Bering Sea--Bristol Bay area. Foul weather, which apparently inhibited feeding between 19 and 23 April 1970, culminated in an intense storm. Similarly in late winter 1969 bad weather in the Irish Sea, combined with strains of molt and perhaps contamination with industrial chemicals, seems to have contributed to mass mortality of the same species (called common guillemot in Britain; Holdgate 1971). The seabird victims of this event had metabolized their body fat and as a result, polychlorinated biphenyls (PCB) and other industrial chemicals passed into livers, kidneys, and brains. Again, a storm at the end of a period of stress seems to have been more than the birds could tolerate.
A further example of a die-off of waterfowl apparently brought on by starvation was given by Barry (1968), who estimated that about 100,000 king eiders _(Somateria spectabilis)_ died when they arrived before the ice broke up in the Beaufort Sea in spring 1964.
Diseases have produced massive die-offs in marine birds. Fowl cholera caused high mortality in nesting common eiders _(Somateria mollissima)_ in the Gulf of St. Lawrence in Quebec (Reed and Cousineau 1967) and in Penobscot Bay, Maine, in the early 1960's (H. Mendall, personal communication). Poisoning from a "red tide" (a bloom of the dinoflagellate _Gonyaulax tamerensis_) caused a die-off of black ducks _(Anas rubripes)_ and herring gulls on the coast of New England in 1972. Similarly a die-off of shags _(Phalacrocorax aristotelis)_ on the east coast of England was caused by a "red tide" (Coulson et al. 1968). During a period of 1 week 90% of the shag nests on the Farne Islands in Northumberland were deserted and about 80% of the breeding population died.
Gradual Declines
When the new volcanic island of Bogoslov emerged in the western Aleutians, Preble and McAtee (1923) reported that it was colonized by large numbers of pigeon guillemots _(Cepphus columba)_, but in the following decades the guillemots have steadily decreased (G. J. Divoky, personal communication). As a further example, the nesting population of Atlantic puffins _(Fratercula arctica)_ in the Atlantic has declined over the past several years, especially those nesting on the Outer Hebrides (Flegg 1972; Harris 1976).
It is difficult to find seabird species whose nesting grounds have not been affected by humans but whose numbers have been censused. The best illustrations of secular changes in relatively constant habitats are probably those available in the British Trust for Ornithology's breeding censuses of songbirds. Songbirds are short-lived and their populations change on relatively short time scales. The northwestern European landscape has remained relatively constant for the last 75 years, yet there are observable decade-long trends--for example, of willow warblers _(Phylloscopus trochilus)_ and dunnock _(Prunella modularis)_. There are detailed data on population changes in great tits _(Parus major)_ through the work of Kluyver (1951), Lack (1964), and Perrins (1965).
Effects Reflecting Environmental Change
Nelson (1966) argued that the increase of gannets in the North Atlantic during this century has been related to increasing temperatures rather than (as usually ascribed) to increased food from fish damaged or escaped during commercial fishing.
Ainley and Lewis (1974) described a particularly interesting example of the effects of environmental change on seabird populations. The events begin with the decrease of seabirds on the Farallon Islands off California as a result of human depredations. Even after fowling was made illegal, the populations of murres, double-crested cormorants _(Phalacrocorax auritus)_, and especially of tufted puffins _(Lunda cirrhata)_ and pigeon guillemots continued to decline as a result of oil pollution. During the last 3 decades the smaller species of seabirds nesting on the Farallons, such as rhinoceros auklets _(Cerorhinca monocerata)_, have increased rapidly and the authors suggest that their increase was abetted by an increase in the small prey fish, northern anchovy _(Engraulis mordax)_. One of course expects predators to be affected by changes in the abundance of their prey. During this same period, larger species of seabirds such as double-crested cormorants and tufted puffins have failed to recover their numbers, and the authors speculate that this failure is related to a decrease of the larger prey fish, Pacific sardine _(Sardinops caerulea)_.
A widely publicized impact of environmental fluctuation upon seabird populations is that of the northeast wind, El Niño, off the Peruvian coast. This wind pushes the upwelling Humboldt Current water offshore and causes mass mortality in the Peruvian anchovies _(Engraulis ringens)_ and, as a consequence, a die-off among the millions of seabirds such as Peruvian guanay cormorants _(Phalacrocorax bougainvillii)_ and Peruvian boobies or piquero _(Sula variegata)_ which feed upon them (Murphy 1936).
Theoretical Considerations
Can useful generalizations be drawn from these observations on population changes? Can a model be constructed of the forces which drive population changes or of population-habitat interactions which keep populations from extinction? Some conflicting theories and assumptions of population dynamics are examined and discussed below.
_The Assumption of Population Stability and of Closely Attuned Density-dependent Mortality_
During the 5 decades before 1970, it was widely accepted that most animal populations were generally stable and saturated before the arrival of the white man. Although a few field biologists vigorously dissented, "establishment" ecologists regarded fluctuations as a departure from the norm, and as such, a hazard to the population. Many theorists of both evolution and ecology argued that adaptations were required to damp fluctuations or the fluctuations would become "random walks" and the population would rapidly become extinct. As a consequence, relatively all theoretical models included stability as a central assumption.
• The basic element of this theoretical complex has been the Lotka-Volterra formula for a logistic curve of population growth and stabilization. According to this formula it has been reasoned that by establishing the inherent rate of increase of a population (i.e., its average natality relative to mortality, or _r_) and by measuring the carrying capacity of the environment (which is the density of the population at saturation, or _K_), one can predict the maximally productive population size, and maximum rate of production of new individuals (or maximum sustained yield). These assumptions have supplied the theoretical framework for virtually all game management and many fisheries practices.
Once stability was assumed, a mechanism for maintaining stability was necessary. This mechanism was found in an interaction between the population and the environment, called density-dependent mortality (Nicholson 1933). The impact of this feedback has been assumed to cause the point of inflection of the "sigmoid curve" and to regulate the density "at equilibrium."
Populations growing in relatively isolated or closed systems have been observed to follow a sigmoid curve toward a steady state. We have data on the growth of several Massachusetts gull colonies which show this type of short-period rapid increase followed by a long sequence of shallow oscillations (Drury and Nisbet 1972). But usually observations have been terminated at about the time the population passed through the point of inflection.
• Lack (1954) accepted the principles formulated by Lotka-Volterra and hence viewed Nicholson's (1933) density-dependence as logically necessary. Lack (1948, 1954) argued that reproductive effort (clutch size or litter size times the number of broods) must be as large as the parents can successfully raise to independence because these biological characteristics are directly subject to natural selection. He argued that because reproductive potential is excessive (Darwin 1859), mortality must be density-dependent if a population is to avoid fluctuations. The only adequately density-dependent regulating process he accepted was the population's response to its food supply (Lack 1954). In fact, for many years Lack rejected Kluyver and Tinbergen's (1953) hypothesis that territory could act as a control on population size in birds because, he argued, territories were compressible and therefore allowed wide fluctuations. To his credit, however, Lack eventually acknowledged this mistake.
The first defect in the concept of "carrying capacity" is the idea that populations have "mechanisms" or "institutions" (Wynne-Edwards 1959) by which the population is kept stable at the carrying capacity in a stable habitat.
The second defect in the concept of carrying capacity is that it presupposes a stable environment. During the early decades of the 20th century most climatologists believed that a departure from the norms of a regional climate set processes in motion which would return the climate to normal. During the last decades, however, climatologists and oceanographers have shown clearly that environments are continuously in flux.
_An Attack on Density-dependent Mortality_
Some theorists rejected the concept of carrying capacity as soon as it was formulated. Andrewartha and Birch (1954) predicted fluctuations would be undamped by inherent population mechanisms but rather would be controlled by external forces indifferent to the density. Their supporting data were drawn from field studies of insects in arid climates. Some of their ideas are directly relevant to seabirds; for example, their assertion that in many cases limits to carrying capacity of the habitat are not set in a way responsive to the density of the population. The number of occupiable ledges on a seabird cliff are fixed and when they are full no more birds can breed there regardless of the amount of food available. For another example, some biological processes act in a way that reinforces fluctuations. Predation can
## act in this way in the relatively closed system of a seabird colony;
i.e., the smaller the prey population the larger the percentage taken by the predators. The importance of predation as a selecting factor is shown by the adaptations marine birds and waterfowl make to avoid it. The fact that large colonies of seafowl are usually concentrated on isolated, predator-free islands is one obvious case (Lack 1966).
Although their ideas are useful in understanding changes in many species, primarily insect populations, the generality of Andrewartha and Birch's (1954) hypothesis is weakened because it conflicts with detailed studies of seabirds which show that in many cases local food resources do limit breeding success. Ashmole (1963) showed this for tropical terns, and Hunt (1972) for some colonies of herring gulls on the New England coast. Nettleship (1972), studying the effects of herring gulls on Atlantic puffins, showed that the effect of harassment and stealing food from the parents was to reduce the amount of food brought to the young and thus reproductive success. In those parts of the colony where gulls were numerous or where the puffins were at a disadvantage in escaping from gulls (i.e., flat rather than steep slopes) the reproductive success of puffins was significantly lower than in areas away from the gulls.
The literal application of Andrewartha and Birch's general ideas also conflicts with observations on subtle adaptations some waterfowl have made to counter predation.
Barry (1967) described the density-avoiding adaptations of arctic-nesting geese to evade predation--specifically by foxes. Black brant _(Branta nigricans)_ nest on low coastal or delta islands seeking to escape by remoteness. Snow geese _(Chen caerulescens)_ are colonial on large, flat areas, seeking protection in numbers. White-fronted geese _(Anser albifrons)_ are solitary nesters on inland swamps, seeking to be "over-dispersed" among scrub willow.
Common eiders, black scoters _(Melanitta nigra)_, tufted ducks _(Aythya fuligula)_, and other ducks select gull colonies as nesting habitat. Although there is little doubt that the ducks choose gull colonies for nesting, there is some doubt as to the reasons. Finnish biologists (summarized by Bergman 1957; Hildén 1965) have concluded generally that gulls protect the duck nests from predation by hooded crows _(Corvus corone)_.
_The Assumption that Fluctuations Are Generally Present_
Recently theorists have built models based on assumptions that fluctuations are a general characteristic of population dynamics, such as Gilpin's (1975) model describing multi-phased oscillations. He took account of the fact that fluctuations (and models) become more complex as more species and nonlinear effects are included. May and Leonard (1975) emphasized that the effect of nonlinearities is to make it impossible to speak even in principle of the equilibrium point of a community. They pointed out that even though the model is deterministic (i.e., assumes that the system will come to equilibrium) the oscillations are so complex that they may appear to be random, and it may be a very long time before the system returns to a position near its starting point. "On the other hand a truly random ecological system could always be fitted by a suitably ingenious limit cycle. This suggests that ecological analysis which does not consider component processes must be viewed with great suspicion" (Gilpin 1975). May and Leonard (1975) and Gilpin are both making a familiar point--that neither the logic nor the interactions described in a formula will describe biological reality unless the assumptions are correct. They are also making a different point--that an ingenious mathematician can create a formula to describe almost any operation (whether its workings are systematic or random), and the formula may seem to work.
Gilpin's moral is that one cannot learn very much that is helpful by studying fluctuations as such. One must study the factors controlling populations. This is a very old idea.
It would appear that defining carrying capacity and inherent rate of increase will not be very instructive in managing seabird populations other than in speculating upon what might be ideal upper limits. It can also encourage the musty sophistry that when a population increases beyond this abstract carrying capacity it "needs" to be hunted to prevent overcropping resources and damage to itself through a population decline. But we will not have the time to carry out detailed studies of life histories seeking for critical population-habitat interactions over several fluctuations for each species involved in a disaster before designing programs to help seabird populations to build up their numbers.
General Characteristics of Marine Birds and Waterfowl
Because general theory does not seem to work and because detailed studies take too much time, I conclude that it is necessary to identify certain general principles upon which to base applied programs. These categories of knowledge include: (1) how vulnerable certain categories of seabirds, waterfowl, and shorebirds are to specific types of disasters, (2) how quickly their numbers build up after they have been reduced, and (3) at what stages we can help them best (i.e., at the breeding grounds, at the winter gathering grounds, or on migration). I believe that we already know enough to design effective programs and to begin work. To this end some characteristics of seabirds are identified which determine the population structures and ways in which their numbers respond to changes in the environment.
_Habitat_
Although the shallow oceans, islands, and seashores are among the most permanent features of the earth in general, the details of their numbers and distribution change rapidly. Sandy shores are obviously being reworked even in the short span of a single lifetime. Distribution of islands and the sediment load, extent, and strengths of currents vary constantly in space and change with time.
The food that seabirds use is patchy and subject to both short-and long-term fluctuations in numbers and shifts in geography. Suitable breeding habitat is scattered, and in many places where oceanic conditions provide a good food supply there are no nesting sites. Consequently, seabirds aggregate in colonies, often dense, and the colonies are clumped for geographical as well as biological reasons.
Lack (1966) discussed some general features of how the breeding adaptations of seabirds are adjusted to the distances the birds must go to find food. The species which feed close to the nest characteristically establish isolated territories or nest in small groups, and they accept many different kinds of nesting substrate. Their clutch sizes are large, individuals move nesting sites readily, and their young grow rapidly compared to the species which feed far at sea. Species which feed far at sea aggregate in large colonies. These species are often rigid in their requirements for suitable nesting sites, their clutches are usually limited to one egg per season, their young grow slowly, and there seems to be strong attachment to traditional colony sites.
_Breeding_
Ashmole (1963) suggested that the clutch size of some oceanic birds is small and colonies occupy only part of the available habitat because food resources within efficient commuting distance of the breeding site are limited. We can see this effect in the usual failure of common terns to raise a third chick, even in the colonies that are surrounded by favorable habitat (Nisbet 1973). Herring gulls whose colonies are close to sources of human refuse raise more young than do those whose colonies are at some distance (Drury 1963; Kadlec and Drury 1968; Hunt 1972).
Ashmole (1963) suggested that during the course of the breeding season the birds exhaust the available food supply. The validity of this suggestion is reflected in the long distances some species (petrels, boobies, murres, dovekies) go for food to feed their young. One would therefore expect that early nesting pairs would be more successful, and this seems to be the case in herring gulls (Nisbet and Drury 1972), kittiwakes (Coulson 1966), and red-billed gulls, _Larus novaehollandiae_ (Mills 1973).
If food is in short supply and parents have to seek over a wide area for food so that they can bring back only a little food at long time intervals, one would expect these birds to have a small clutch and their young to grow slowly, as is the case. One would also expect seabird colonies situated near oceanic currents to be larger and more successful because food is continuously renewed. Conversely, one would expect colonies next to still waters to be smaller and less successful.
The small clutch size of seabirds means that when a population has been reduced, it will grow slowly toward its former abundance. The growth rates of seabird populations on the New England coast since their release from human predation reflects this. Species such as black guillemots with only two eggs per clutch and herring gulls with three eggs per clutch have increased more slowly than have the populations of common eiders or double-crested cormorants both with three to six eggs per clutch (Drury 1973).
If the species that nest in colonies show a high degree of site tenacity, they are not likely to reestablish a colony after it has been eliminated. An exception to this is the food subsidy provided by man, which seems to have been important in creating a nonbreeding population of herring gulls large enough to form a "critical mass" for the formation of a new gullery.
_Age Structure_
Because the main element of population size--the number of breeding adults--is limited by the number of breeding colonies and the food available to those colonies, one assumes that the total numbers of seabirds is much less than could be supported by the larger areas of productive oceans. Hence one suspects that there is lessened competition for food outside the breeding season and that lack of competition for food is a major reason for seabirds being long-lived, often to extremes little suspected until recently. Mortalities of 10-12% per year are common, and some as low as 4% (wandering albatross, _Diomedea exulans_; Tickell 1968) have been recorded.
In contrast, songbirds with large clutches, such as the titmice studied by Kluyver (1951), produce a large number of young with whom they and other adults must compete for food during the winter period of food shortage. Because the titmice are permanent residents, they occupy all of the available habitat throughout the year. Hence titmice suffer intense intraspecific competition, which shortens the survival of adults. Kluyver's experiments (1966) with nest boxes used by a closed population of great tits on Vlieland, The Netherlands, showed that by artificially reducing clutch size the survival of adults was increased.
Similar competition for the few territories available on marshes and consequent shortened life expectancy, can be expected in waterfowl with large broods. The effect should be less marked for geese with smaller clutches that nest in less confined habitats.
The long life span of seabirds means that a population will have a large component of older age categories; this characteristic has several implications:
• It means that the population can survive years of reproductive failure without the observable immediate effects that would be manifest in titmice, grouse, or rabbits. Near failure of reproduction during a breeding season among arctic seabirds at Bear Island was reported by Bertram et al. (1934). Many similar observations have been made since then: Pitelka et al. (1955) reported such a case among skuas and gulls at Point Barrow, Drury (1961) for greater snow geese _(Chen cerulescens atlantica)_ at Bylot Island, Jones (1970) for black brant gathering at Isambek Lagoon on the Alaska Peninsula, and D. A. Snarski (personal communication) for kittiwakes at Cook Inlet. Reproductive failure can sometimes be chronic, as observed by Nisbet (1972) for terns at Cape Cod, Massachusetts, or by Drury (1963) and Hunt (1972) for herring gulls on the outer islands on the coast of Maine.
When reproductive failure becomes chronic as observed on peregrine falcons _(Falco peregrinus)_ by Hickey (1969) and in ospreys _(Pandion haliaetus)_ by Ames and Mersereau (1964), the population of adults may hold on for a number of years without evident decline. Damage to the structure of the whole population may be serious before any numerical results are evident.
• Although there may not be intensive competition for food in the habitat away from breeding colonies, there is intense competition for food and breeding sites at and around the colonies. Hence age and previous experience in seabirds assume importance in establishing territory and in breeding success. Associated with this is the tendency for immature birds to delay breeding until they are several years old and for the immatures to remain on feeding grounds at some distance from the colonies. In some cases young birds may "hang around" breeding colonies and even feed some of the young. When young birds do first breed they usually lay smaller clutches and raise fewer young than do older birds. The importance of age and experience upon breeding success has been well documented for kittiwakes (Coulson 1966) and red-billed gulls (Mills 1973).
The fundamental biological importance of this delayed maturity seems to be emphasized by the persistence for several years of immature plumages, so clearly identifiable that even a human observer can recognize the age of an individual. One assumes such an evident feature must have adaptive significance.
_Wintering Grounds_
When colonial nesting seabirds leave their breeding islands for their wintering grounds, their identification with that island is lost as far as population effects are concerned, because birds from many colonies mingle on the wintering grounds. Major mortality takes place on the wintering grounds and must therefore act on the species population as a whole rather than differentially on individuals associated with especially dense colonies. Such a direct relation between colony density and mortality would be necessary for density-dependent mortality to regulate the number of birds on a breeding colony. Conversely, one cannot expect that all colonies will decrease equally because mortality should be equally distributed if all the population gathers on a common wintering ground. Thus density-dependence acts only in a very general way upon the sum of animals considered as an abstract entity--the population.
In fact, on the wintering grounds, as shown by a graph of numbers of gulls reported on Christmas Counts on Cape Cod, Massachusetts (Kadlec and Drury 1968), herring gulls are very responsive to local conditions and move several tens of miles to gather at favorable feeding sites. An aerial survey of the gulls on the East Coast of the United States (Kadlec and Drury 1968) showed that more than half of the gulls were gathered near major food sources in large metropolitan districts. Most of the remainder were gathered near small fishing ports. Very few were scattered along the shoreline in what one assumes is the traditional gull habitat. Later analyses of the relation between the distribution of banding recoveries of birds in their first winter and the distribution of immatures as found on this winter census (Drury and Nisbet 1972) suggested that proportionately more first-year gulls died in those areas where the birds were sparsely distributed than died in the crowded metropolitan areas.
These results suggest both that there is not a direct feedback between reproductive rate and mortality, and that mortality may even be inversely density-dependent on wintering grounds. This last runs counter to traditional ecological ideas that density causes a change in mortality rate. The idea that individuals gather where "living is easy" and mortalities are low is consistent with the theory of natural selection. One would not expect the food of the gulls to be evenly distributed, and one would expect individuals to move away from areas where food is scarce and mortality is high.
_Differences in Breeding Success Between Colonies_
Breeding success has been shown to vary among individual pairs of gulls (Drost et al. 1961). Certain groups of individuals nesting in patches within a single colony have greater breeding success than do others (Coulson 1968; Drury and Nisbet, in preparation). Differences in breeding success also occur between colonies (Frazer-Darling 1938; Kadlec and Drury 1968; Drury and Nisbet 1972). Some colonies reproduce consistently better than others--for example, the gull colonies close to fishing ports and metropolitan areas. Other colonies produce consistently fewer young, such as the colonies on the outer islands in the Gulf of Maine (Drury 1963; Kadlec and Drury 1968; Hunt 1972). The populations of successful colonies grow while the numbers of unsuccessful colonies decline, even during a period of general population increase (Kadlec and Drury 1968).
The difference between success and failure, growth and decline, appears to lie in the food available. Colonies increase where breeding success is high and decrease where breeding success is low. One important reason seems to be that adult gulls may move to a more productive colony even after they have nested with another colony (Drury and Nisbet 1972; Kadlec 1971). Such adaptations can be viewed as adjustments by which individuals meet the requirements of an environment in which the availability of food and other necessities is patchy and shifting.
_Dispersal_
In general terms, the willingness of some individuals to disperse while the majority of individuals remain loyal to a colony can be considered a major mechanism of population maintenance. If conditions deteriorate seriously at one place so that the local populations decline or disappear, dispersal from other centers can be expected to repopulate the area as soon as local conditions again become suitable. This subject has been treated in more detail by Drury and Nisbet (1972) and Drury (1974_b_).
Occupation of new, or return to former, nesting sites has been recorded in detail for fulmars _(Fulmaris glacialis)_ by Fisher (1952) and for herring gulls by Kadlec and Drury (1968). Dispersal is also known for waterfowl. Hansen and Nelson (1957) reported that of some 8,000 brant banded in midsummer on the Yukon delta 8 were recovered in northern Siberia and 28 in northern Alaska and arctic Canada. They suspected that pairing on the wintering grounds was responsible for the change in breeding areas, a change that would not be expected among other North American species of geese. Similarly, wide dispersal seems to occur in pintails _(Anas acuta)_, mallards _(Anas platyrhynchos)_, and wood ducks _(Aix sponsa)_.
The general tendency for some individuals to disperse and the frequency of "extra limital" breeding attempts is especially well established in the Bering Sea region, in part at least because vagrants from Siberia or North America are readily identified as such. In the Aleutian Islands, Emison et al. (1971) and Byrd et al. (1974) have enumerated the nesting vagrants. For the Pribilof Islands, Kenyon and Phillips (1965), Sladen (1966), and Thompson and DeLong (1969) have recorded the repeated appearance of birds of Siberian distribution, and Fay and Cade (1959) and Sealy et al. (1971) did the same for St. Lawrence Island.
One can conclude that a few individuals are constantly trying to settle in new geographical areas. As climatic and habitat conditions change, some populations are able to become established; for example, southern species such as mockingbirds _(Mimus polyglottus)_, cardinals _(Cardinalis cardinalis)_, and tufted titmice _(Parus bicolor)_ have settled in southeastern New England during the last 2 decades. These southern species have received much publicity. But at the same time, a less publicized dispersal of white-throated sparrows _(Zonotrichia albicollis)_, hermit thrushes _(Catharus guttatus)_, and dark-eyed juncos _(Junco hyemalis)_ has resulted in new nesting records of more northerly species, also in southeastern New England.
The ability (or lack of ability) of some organisms to expand their ranges over time has been a subject of consideration for a number of years by plant and animal geographers. An important botanical paper on this subject in the Bering Sea region was presented by Hultén (1937), who analyzed the ranges of plants of the area of Kamchatka, eastern Siberia, Alaska, and northwest Canada, showing that diverse floras occur in some restricted geographic areas. He called these areas "refugia," and postulated that many species had survived Pleistocene glaciations in them because these refugia remained ice-free. He, like Fernald (1925), was puzzled as to why only certain species had been able to expand their ranges outward from these "areas of persistence," while other apparently more "conservative" species were unable to do so. Similarly, there appear to be conservative endemic bird species of the Bering Sea region: the extinct Commander Islands cormorant _(Phalacrocorax perspicillatus)_, Steller's eider _(Polysticta stelleri)_, spectacled eider _(Lampronetta fisheri)_, emperor goose _(Philacte canagica)_, whiskered auklet _(Aethia pygmaea)_, least auklet _(A. pusilla)_, parakeet auklet _(Cyclorrhynchus psittacula)_, Aleutian tern _(Sterna aleutica)_, red-legged kittiwake _(Rissa brevirostris)_, bristle-thighed curlew _(Numenius tahitiensis)_, long-billed dowitcher _(Limnodromus scolopaceus)_, surfbird _(Aphriza virgata)_, black turnstone _(Arenaria melanocephala)_, rock sandpiper _(Calidris ptilocnemis)_, and western sandpiper _(C. mauri)_.
The ranges of horned puffins _(Fratercula corniculata)_, Kittlitz's murrelet _(Brachyramphus brevirostris)_ and, perhaps, crested auklet _(Aethia cristatella)_ suggest that some species of "Beringian" seabirds have expanded their ranges from Hultén's (1937) "refugia."
_Dispersal and Regional Persistence of Marginal Populations_
The presence of several sub-elements of a species population and, therefore, the opportunity for dispersion among alternative breeding sites may be an important factor in the regional persistence of a species on the margin of its range, as illustrated by the history of laughing gulls _(Larus atricilla)_ in New England.
Between 1875 and 1900 there were fewer than 50 laughing gulls in Massachusetts (Mackay 1893) and about 35 in Maine (Norton 1924). In Massachusetts the laughing gulls all settled on one large island, Muskeget, where by 1940 there were about 20,000 pairs (Noble and Würm 1943). Meanwhile, in Maine the population had been disturbed by sheep and men and had shifted about among seven islands. The Maine population grew to only about 350 pairs by 1940 (Palmer 1949).
The laughing gull population in both States has decreased since 1940. In Massachusetts, where all pairs occupied one island, the population had fallen to about 250 pairs by 1972, but the Maine population, still divided into five colonies, stabilized at 250 pairs (i.e., the same as instead of only 1% of the Massachusetts population).
Use of General Principles in Solving Conservation Problems
Game biologists have successfully maintained the populations of hunted animals by using a number of classical principles of game management. They have controlled mortality by regulating kill and have increased standing stock by improving habitat on a local scale. This seems to have worked in species which are short-lived, have large clutch sizes or litters, and which occupy mosaics of highly productive "successional habitat." Seabirds, however, contrast with these species in a number of important biological characteristics. They have small clutches, postpone breeding until they are several years old, and are subject to periodic or chronic reproductive failures. Therefore, their populations are skewed toward older animals and replacement of lost individuals is slow. Many seabirds, like some geese, have a high level of site tenacity and thus may resist recolonization or fail in the attempt to recolonize a breeding site once eliminated from it. In those species studied it appears that the breeding birds at a small percentage of colonies are responsible for a large proportion of the annual crop of young. It is probably dangerous, therefore, to risk either damage to or elimination of well-established colonies.
Studies of kittiwakes by Coulson and White (1958, 1961), sooty terns _(Sterna fuscata)_ by Ashmole (1963) and Harrington (1974), Atlantic puffins by Nettleship (1972), and Cassin's auklets _(Ptychoramphus aleutica)_ by Manuwal (1974), and the practice of eider "farming" in Iceland indicate that the number of available territories or breeding sites may limit the size of a population and that populations can be increased by increasing the number of sites available. This suggests one way in which direct steps can be taken to encourage the numbers of breeding seabirds. Other studies indicate that seabirds will move into synthetic habitat such as created by the window ledges on buildings (Coulson and White 1958) or the islands created by dumping spoil from channel dredging operations (Buckley and Buckley 1971, 1975; Soots and Parnell 1975).
Most generalizations of population biology have been derived from the study of insects, songbirds, or game species. It seems inadvisable to assume that those principles will apply to seabirds without modification. For example, predation by gulls and ravens may have a disastrous effect on a seabird colony at low colony density but have progressively less impact as the colony size and density increase. Fox predation may have important effects over most ranges of prey density because the presence of foxes has important psychological effects.
The habitats of seabirds include elements in which birds are widely dispersed (feeding areas) and others in which birds are crowded and narrowly localized (nesting sites). Thus effective programs of conservation should include guarantees that a number of colony sites be available in as widely dispersed a pattern as possible. Each productive feeding ground should, if possible, have several colony sites available.
We have argued elsewhere (Drury and Nisbet 1972; Drury 1974_a_) that one of the chief defenses any population has against extinction is the combination of being divided into a number of population centers with having some movement of individuals between the centers, but not too much. Because it is highly improbable that a single catastrophe will affect more than a part of a species' range at any time, the more numerous and widely scattered the partially independent segments of a population are, the better the species is insured against extinction. This, of course, suggests that the size of each colony may be less important for long-term survival than is the total number of colonies.
One intuitively concludes that "conservative" species, such as those endemic to the Bering Sea region (whose dispersal and colonizing mechanisms seem to be poorly developed), are especially vulnerable to the effects of local population crashes. These "local" species therefore deserve special consideration.
I would like to emphasize two points to be included in designing a "management" program:
• It seems that the most promising management techniques will be built upon ensuring the health of colonies and the associated feeding areas at which reproductive success is high enough to "export" young. Thus it is useful to identify those colonies which are exporting young and to give special care to their preservation. As populations of prey species change locally, so will the success of the local nesting birds. A colony which is thriving at one time may be barely maintaining itself at another (Ainley and Lewis 1974), or it may decrease, as in the case of "guano birds" during El Niño years in the Peru Current.
• Because centers of abundance of marine birds shift (Fisher 1952; Drury 1963, 1974_a_), it will be prudent to plan for large areas and over long periods of time. Harrison Lewis, a pioneer in seabird management in eastern Canada, said (personal communication) that just as soon as he got approval of a new seabird sanctuary through the long corridors of the distant government bureaucracies in Ottawa, the birds would move to a new island and he had to start the process all over again.
The objective is to maintain a variety of colony sites for populations to move among as local patterns of productivity in the shallow sea shift.
Goals for Research on Population Dynamics of Seabirds for Purposes of Conservation
1. To learn the distribution and relative importance of seabird colonies, the number of pairs nesting and nonbreeding individuals at each colony, and the timing of breeding activities for each geographical region. The most important step toward conserving marine birds is to get public ownership and protection for their breeding grounds.
2. To understand the life cycle of key species. Three needs are clear:
a. To identify key species whose biological characteristics can conveniently be studied and measured. Studies of these species may be useful in monitoring the "health" of seabird breeding areas.
If it is established that the reproductive success of certain species varies similarly in response to changes in their marine habitat (such as black-legged kittiwakes and horned puffins), one could use key species (black-legged kittiwake) to assess the performance of those species in a colony whose breeding success is difficult to measure (horned puffin).
b. To develop efficient and practical ways of censusing and measuring productivity of crevice-, scree-, and hole-nesting species such as puffins and auklets.
c. To establish annual differences in reproductive success and mortality rates by age classes of the key species, and from these to identify rates of population turnover so as to be able to predict the effects of mass mortalities.
3. To learn enough about the differences in behavior and productivity among colonies to establish which colonies produce surplus young and which have low productivity. At first, maximum efforts for conservation should be concentrated at those sites which produce surplus young.
4. To learn about colonial behavior. Two needs are apparent:
a. To know enough about the lives of individually marked birds of known age so as to be able to infer the behavior of population elements at all stages of their life cycle.
b. To know enough about the lives of subadult birds to understand what proportion of subadults visit and become established at breeding sites, why the subadults visit the breeding sites and what effect their presence has on the territories and breeding success of their neighbors and biological relatives.
5. To know enough about places where seabirds, waterfowl, and shorebirds gather on migration and during the winter to identify those areas which need special protection from effects of economic development.
a. It is important to determine the areas where marine birds gather at sea when they are away from their breeding grounds. What factors of habitat and food supply make certain places preferable to others? What is the relation between gathering grounds and underwater topography (banks and edges of the continental shelf)? What are the seasonal and annual differences in preferred gathering grounds? What special hazards exist, such as unusual extent of sea ice or exceptional storms?
b. It is important to plot coastal areas where waterfowl and shorebirds gather on migration, for molting, and during the winter. Which open leads in the ice and patches of open water at the mouths of rivers are of especial importance in spring? What shorelines and beaches act as "leading lines" during migration? Which capes and points result in concentrated overflights of migrating waterfowl, and hence are locations of unusually high kills by hunters? What wetlands, bogs, coastal ponds, lakes, and lagoons are used as gathering grounds and to what extent do waterfowl and shorebirds exchange between gathering grounds? How much redundancy of wetlands is needed to make the wetlands system maximally productive for waterfowl and shorebirds?
Answers to these questions will identify which geographic areas deserve special protection during development. The answers will also identify the kinds of influences which might lower the contribution of each critical area to the survival of seabirds, waterfowl, and shorebirds. Areas identified as important under these categories must be included in policy decisions related to land-use planning and management.
6. To learn more about the effects of varying quantities of food on breeding behavior and performance:
a. What are the effects of food abundance in early spring on date of laying, clutch size, and egg size?
b. What effects do storms have at different stages of the reproductive schedule?
c. What effects do quantitative and qualitative (species composition of prey) changes in food supply have on the survival of chicks?
d. What are the similarities and differences between what parents eat and what they feed their chicks?
Although this is important basic biological knowledge, it contributes little to conservation efforts because food differences result from changes in the ocean over which humans can have little effect.
7. To learn more about prey species and their availability to marine birds:
a. To know more about the breeding areas, reproductive rates, growth rates, and routes of dispersal of the major prey food species. In most areas a few species of teleost fish (e.g., _Ammodytes_) or Crustacea (e.g., copepods, euphausids, mycids, or amphipods) make up most of the food of marine birds. Yet, the barest minimum is known about the biology of such species. A good first estimate of the "condition" of the marine environment can probably be made by measuring reproductive rates and growth rates of these key prey species. Hence an efficient (though indirect) way to measure those rates may be by monitoring reproduction of birds.
b. To know more about the density and distribution of key prey items season by season, and to learn more about the relation of their abundance and distribution to their availability to birds, as Bédard (1969) showed for _Calanus_ to least auklets, and _Thysanoessa_ to crested auklets.
There are some indications that the population size of prey items can vary widely without having a marked effect on the numbers of their predators. Does commercial fishing for the large, predatory fish have a measurable effect on the food available to marine fish? Do the large pollock and salmon fisheries (high seas) make zooplankton available to smaller alcids? Do marine birds affect a fishery?
c. To know more about the oceanography of continental shelf waters, more specifically the waters between 6 and 60 m deep. The shallow waters of continental shelves are some of the most productive of sea waters, but are among the least studied. Although some species (black-legged kittiwakes, tufted puffins, and fulmars) move into deep waters, many species of marine birds of northern waters gather in large numbers on preferred feeding grounds at or near the edges of continental shelves during their winter season (Fisher 1952; Tuck 1960).
8. To know more about the potential effects of proposed developments on seabirds and waterfowl.
a. To prepare models which will predict probabilities of contamination of breeding and feeding areas (summer, winter, and during migration) using existing knowledge of
(1) areas of proposed mineral development;
(2) areas that will be influenced by secondary development such as dredging new harbors, laying subsurface pipelines;
(3) tidal and oceanic currents;
(4) numbers of marine birds or waterfowl using specific geographic areas and habitats (e.g., waters below nesting cliffs, feeding grounds, wintering grounds, and gatherings during migration);
(5) the distribution and patchiness of habitats (i.e., the redundancy among and within habitats and the degree to which populations exchange between alternative habitats);
(6) the biological importance of species in local ecosystems (Are they predators whose effects increase diversity?);
(7) the human importance of the species (Are they endemics? Do they have unusual "charisma" for the public?);
(8) the vulnerability of the species (Is its distribution restricted? Is it subject to oil pollution? Are their preferred grounds near areas of high development potential?);
(9) the types of biological effects (e.g., oil contamination of plumage, PCB contamination of food chains); and
(10) whether the potential impacts are reversible or irreversible and to what degree.
b. To understand more of the effects of hunting on the behavior of marine birds and waterfowl on their breeding grounds, and to assess the effects on breeding performance of changes in behavior which result from human activities (such as hunting or studying the birds).
c. To understand the effects of the presence of predators (whether introduced or native) on breeding colonies in order to assess the importance of removing the predators or preventing their access to breeding grounds.
The Relation of the Products of Biological Research to Programs for Conservation of Marine Bird Resources
Although peaceful coexistence of wildlife populations and economic development are here assumed to be practical, some new social institutions are needed to control damaging activities of people during economic development. Human activities and industrial products which damage wildlife or their habitat must be identified, as must the space and resources which wildlife require for survival and health.
1. What seabird cliffs, islands, lagoons, wetlands, river mouths, and other habitat features are of first importance for breeding or for maintaining the populations? Some small areas of habitat are critical for the survival of some species during periods of stress. Those habitats need official recognition. Steps are needed to ensure that the habitats are maintained.
2. What physical expressions of economic development are of little, modest, or serious impact on wildlife and its habitat? These activities and constructions include harbors, storage sites, transshipment facilities, roads, pipelines, summer camps, and suburban or vacation developments.
3. What kinds of human activities will disturb, damage, or change the behavior or accessibility of wildlife? Many activities of one group of people have secondary effects which affect the enjoyment of resources for other groups. These include
a. gill netting for salmon, which may kill large numbers of murres and diving ducks;
b. release of predators on seabird nesting islands, which may kill adults or inhibit their feeding their young;
c. free running of pets (such as dogs and cats) over wetlands or wildlife habitat, because pets are predators and harass the wildlife which may be feeding;
d. flights of aircraft, especially helicopters, near or over seabird cliffs because such flights may cause serious damage to eggs and young;
e. hunting, because the game becomes timid and flees from those who might enjoy watching wildlife;
f. snow machines, because their presence is disagreeable to many and they provide easy access by which disturbing activities may reach into areas where wildlife would otherwise be undisturbed.
4. What limitations or alterations are needed in the existing legal institutions, such as the Marine Mammals Protection Act, the instruments implementing native land claims, the process of Alaska State lands withdrawal, the conditions for leasing State and Federal lands for development of mineral resources, and traditional rights of private property? All of these legal institutions are relevant to problems of wildlife survival and restoration, and within most of these institutions there exist conflicts between rights and benefits of special political interests and the husbanding of renewable common property resources.
Experience in Europe and in New England suggests that if reasonable limitations are set on human activities and that if adequate money charge is made against those who profit by economic development to defray full social costs, wildlife can continue to do well. In most cases where damage has occurred it is because those who administer the public institutions have failed to include consideration of the common property resources.
References
Ainley, D. G., and T. J. Lewis. 1974. The history of Farallon Island marine bird populations. Condor 76(4):432-446.
Ames, P. L., and G. S. Mersereau. 1964. Some factors in the decline of the osprey in Connecticut. Auk 81(2):173-185.
Andrewartha, H. G., and L. C. Birch. 1954. The distribution and abundance of animals. Univ. Chicago Press, Chicago, Ill. 782 pp.
Ashmole, N. P. 1963. The regulation of numbers of tropical oceanic birds. Ibis 103b:458-473.
Bailey, E. P., and G. H. Davenport. 1972. Die-off of common murres on the Alaska Peninsula and Unimak Island. Condor 74(2):215-219.
Barry, T. W. 1967. Geese of the Anderson River delta, Northwest Territories. Ph.D. Thesis. Univ. of Alberta, Edmonton, Alberta, Canada. 176 pp.
Barry, T. W. 1968. Observations on natural mortality and native use of eider ducks along the Beaufort Sea Coast. Can. Field-Nat. 82(2):140-144.
Bédard, J. 1969. Feeding of the least, crested, and parakeet auklets around St. Lawrence Island, Alaska. Can. J. Zool. 47:1025-1050.
Belopol'skii, L. O. 1961. Ecology of sea bird colonies of the Barents Sea. (Translated from Russian.) Israel Program for Scientific Translations, Jerusalem. 346 pp.
Bent, A. C. 1919. Life histories of North American diving birds. U.S. Natl. Mus. Bull. 107. 245 pp.
Bent, A. C. 1921. Life histories of North American gulls and terns. U.S. Natl. Mus. Bull. 113. 345 pp.
Bent, A. C. 1922. Life histories of North American petrels and pelicans and their allies. U.S. Natl. Mus. Bull. 121. 343 pp.
Bergman, G. 1957. Concerning the problem of mixed colonies: the tufted duck and gulls. Die Vogelwarte 19(1):15-25.
Bertram, G. C. L., D. Lack, and B. B. Roberts. 1934. Notes on East Greenland birds, with a discussion of the periodic non-breeding among arctic birds. Ibis 13(4):816-831.
Brown, R. G. B. 1967. Breeding success and population growth in a colony of herring and lesser black-backed gulls _Larus argentatus_ and _L. fuscus_. Ibis 109(4):502-515.
Buckley, F. G., and P. A. Buckley. 1971. The breeding ecology of royal terns _(Sterna [thalasseus] maxima maxima)_. Ibis 114(3):344-359.
Buckley, P. A., and F. G. Buckley. 1975. The significance of dredge spoil islands to colonially nesting waterbirds in certain national parks. Proc. Conf. on Management of Dredge Islands in North Carolina Estuaries, May 1974. N.C. Sea Grant Publ. UNC-SG-75-01, Raleigh.
Byrd, G. V., D. D. Gibson, and D. L. Johnson. 1974. The birds of Adak, Alaska. Condor 76(3):288-300.
Coulson, J. C. 1966. The influence of the pair-bond and age on the breeding biology of the kittiwake gull _Rissa tridactyla_. J. Anim. Ecol. 35:269-279.
Coulson, J. C. 1968. Differences in the quality of birds nesting in the centre and on the edges of a colony. Nature 217 (Feb. 3):478-479.
Coulson, J. C. 1974. Kittiwakes _Rissa tridactyla_. Pages 134-141 _in_ S. Cramp, W. R. P. Bourne, and D. Saunders, The Seabirds of Britain and Ireland. Taplinger Publ. Co., Inc., New York. 287 pp.
Coulson, J. C., G. A. Potts, I. R. Deans, and S. M. Fraser. 1968. Exceptional mortality of shags and other seabirds caused by paralytic shellfish poison. Brit. Birds 61:381-404.
Coulson, J. C., and E. White. 1958. The effect of age on the breeding biology of the kittiwake _Rissa tridactyla_. Ibis 100(1):40-51.
Coulson, J. C., and E. White. 1961. An analysis of the factors influencing the clutch-size of the kittiwake. Proc. Zool. Soc. Lond. 136:207-217.
Cramp, S., W. R. P. Bourne, and D. Saunders. 1974. The seabirds of Britain and Ireland. Taplinger Publ. Co., Inc., New York. 287 pp.
Darwin, C. 1859. On the origin of species by means of natural selection. John Murray, London. 490 pp.
Dement'ev, G. P., R. N. Meklenburtsev, A. M. Sudilovskya, and E. P. Spangeberg. 1968. Birds of the Soviet Union. Vol. 2. (Translated from Russian.) Israel Program for Scientific Translations, Jerusalem. 553 pp.
Drost, R., E. Focke, and G. Freytag. 1961. Entwicklung und aufbau einer population der Silbermöwe, _Larus argentatus argentatus_. J. Ornithol. 102(4):404-429.
Drury, W. H. 1961. Observations on some breeding water birds on Bylot Island. Can. Field-Nat. 75(2):84-101.
Drury, W. H. 1963. Results of a study of herring gull populations and movements in southeastern New England. Pages 207-217 _in_ Colloque: Le problème des oiseaux sur les aérodromes (Nice, 1963). Inst. Nat. Rech. Agron., Paris.
Drury, W. H. 1973. Population changes in New England seabirds. Bird-Banding 44(4):267-313.
Drury, W. H. 1974_a_. Population changes in New England seabirds. Bird-Banding 45(1):1-15.
Drury, W. H. 1974_b_. Rare species. Biol. Conserv. 6(3):162-169.
Drury, W. H., and I. C. T. Nisbet. 1972. The importance of movements in the biology of herring gulls in New England. Pages 173-212 _in_ Population Ecology of Migratory Birds: a Symposium. U.S. Fish Wildl. Serv. Wildl. Res. Rep. 2. 278 pp.
Dutcher, W. 1901. Results of special protection to gulls and terns obtained through the Thayer Fund. Auk 18(2):76-103.
Dutcher, W. 1904. Report of the A.O.U. Committee on the Protection of North American Birds for the year 1903. Auk 21(suppl.):97-208.
Emison, W. B., F. S. L. Williamson, and C. M. White. 1971. Geographical affinities and migrations of the avifauna on Amchitka Island, Alaska. BioScience 21(12):627-631.
Fay, F. H., and T. J. Cade. 1959. An ecological analysis of the avifauna of St. Lawrence Island, Alaska. Univ. Calif. Publ. Zool. 63:73-150.
Fernald, M. L. 1925. Persistence of plants in unglaciated areas of boreal America. Mem. Am. Acad. Arts Sci. 15:239-342.
Fisher, J. 1952. The fulmar. Collins, London. 496 pp.
Fisher, J., and R. M. Lockley. 1954. Seabirds: An introduction to the natural history of the seabirds of the North Atlantic. Houghton Mifflin Co., Boston. 320 pp.
Fisher, J., and H. G. Vevers. 1943. The breeding distribution, history and population of the North Atlantic gannet _(Sula bassana)_.