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Spatial relationships between predators and prey have important implications for landscape processes and patterns. Highly mobile oceanic birds and their patchily distributed prey constitute an accessible model system for studying these relationships. High-frequency echosounders can be used together with simultaneous direct visual observations to quantitatively describe the distributions of seabird consumers and their resources over a wide range of spatial scales, yielding information which is rarely available in terrestrial systems. Recent fine-scale investigations which have used acoustics to study the distribution of foraging marine birds have reported weak or ephemeral spatial associations between the birds and their prey. These results are inconsistent with predictions of optimal foraging, but several considerations suggest that traditional foraging models do not adequately describe resource acquisition in marine environments. Relative to their terrestrial counterparts, oceanic 'landscapes' are structurally very simple, but they generally lack visual cues about resource availability. An emerging view assumes that perceptually constrained organisms searching for food in multiscale environments should respond to patterns of resource abundance over a continuum of scales. We explore fractal geometry as a possible tool for quantifying this view and for describing spatial dispersion patterns that result from foraging behavior. Data on an Alaskan seabird (least auklet [Aethia pusilla]) and its zooplanktonic food resources suggest that fractal approaches can yield new ecological insights into complex spatial patterns deriving from animal movements. © 1992 SPB Academic Publishing bv.

During a three month research cruise near the island of South Georgia, sea surface temperature (SST) increased from c. 2°C to over 4°C. Satellite derived SST show that this corresponded to a rapid southward and eastward shift of isotherms in the northern Scotia Sea, which could have resulted from changes in the wind field. At the same time, observation from the ship of seabirds close to the island indicated changes in the abundance of some non-resident species, whereas resident breeders from South Georgia, such as black-browed albatrosses (Diomedea melanophris) and prions (Pachyptila spp.) which were foraging locally, were present at consistent density in both halves of the survey. Blue petrels (Halobaena caerulea) left the area after breeding, so were associated only with the low water temperatures during the first part of the cruise. In contrast, great shearwaters (Puffinus gravis) and soft-plumaged petrels (Pterodroma mollis) migrated into the area later in the survey. These birds were almost certainly non-breeders which were feeding in the warmer water which had moved towards the island. © 1992, Antarctic Science Ltd. All rights reserved.

We used five transects radiating from the South Orkney Islands to describe the distribution and abundance of marine birds during three days in late summer 1983. We found elevated numbers of birds at most crossings of steep physical gradients (fronts), but species were not equally attracted to each front. Our data suggest that the fronts around the South Orkney Islands, especially the Weddell-Scotia Confluence, provide important foraging habitat for birds. Albatrosses and fulmars appeared to aggregate preferentially near fronts overlying the insular slope, whereas Chinstrap Penguins were most abundant over the shelf. © 1992 Springer-Verlag.

Uria aalge and U. lomvia were concentrating over a dense epibenthic sound-scattering layer near the ridge crest on southward ebb tide currents. Samples taken through the layer contained high numbers of euphausiids (Thysanoessa inermis and T. raschii). Stomachs of murres collected in the area contained predominantly euphausiids. -from Authors

Examined Eudyptes chrysolophus, Arctocephalus gazella and their zooplankton prey, in particular Antarctic krill Euphausia superba in February 1986. Antarctic fur seals and macaroni penguins showed positive correlations with Antarctic krill density across a wide range of spatial scales. When the influences of distance and direction on predator abundance were factored out, the authors were able to demonstrate an influence of Antarctic krill abundance at measurement scales between 10-100 km for Antarctic fur seals and for macaroni penguins at the scale of 70-100 km. Water depth was an important correlate of Antarctic krill and Antarctic fur seal abundances but not of the abundance of macaroni penguins. -from Authors

The distribution and abundance of breeding and foraging seabirds is usually a reflection of the availability of prey in the marine ecosystems on which the birds depend. At the scale of hundreds of km, differences in marine communities may be reflected in variation in the species composition of resident seabirds. At small scales, environmental features such as fronts or ice can influence where birds will aggregate to forage. Features at which prey become concentrated near the surface are of particular importance to bird species dependent upon small planktonic organisms. Concentrations of foraging seabirds frequently indicate the presence of such features, or of areas of unusually high prey biomass. The absence of birds does not mean that concentrations of potential prey are absent. “Assembly rules,” by which one might predict aspects of the marine environment that birds should use in selecting foraging areas are proposed. Copyright © 1991, Wiley Blackwell. All rights reserved

In the Antarctic, seabird species distributions are annular or latitudinal, with strong similarities in species composition of seabird communities in all ocean basins at a given latitude. In the Arctic, communities are arranged meridionally, and show strong differences between ocean basins and, at a given latitude, between sides of ocean basins. In the Antarctic, much seabird foraging is over deep water, and within-season, small-scale patchiness in prey abundance and availability in ice-free waters is likely to be controlled primarily by the behavior of the prey, rather than by physical features. Thus, prey availability may be unpredictable in time and space. In the Northern Hemisphere, most seabird foraging is concentrated over shallow continental shelves, where currents interact with bathymetry to produce predictable physical features capable of concentrating prey or making prey more easily harvested by seabirds. Ice cover appears to be the most important physical feature in the Antarctic. An entire community of birds is specialized to use prey taken near the ice edge. The open-water portion of the marginal ice zone is also an important foraging habitat. In the Arctic, a food web based on underice algae is used by marine birds, but few data exist on avian use of the open water segment of the marginal ice zone. Only rarely does the small-scale abundance of birds match that of their prey; correlations between predators and prey are generally stronger at larger scales. In the Antarctic, largest aggregations of krill may be disproportionately important to foraging seabirds. -from Author

We studied the distribution and abundance of marine birds in Bransfield Strait and southern Drake Passage during January and February 1985. We identified clusters of bird species, "communities" with similar distributions, and examined the extent to which the distributions of these seabird communities reflected the underlying physical oceanography of the region. Based on temperature, salinity and silicon data, we identified 11 water masses which resulted from varying degrees of mixing of water from the Pacific Basin, the Bellingshausen Sea, the Weddell Sea and terrestrial runoff. Seabird species assemblages were associated with contiguous clusters of water masses, suggesting a response by the birds to apparently subtle differences in their marine habitat. © 1990.

Investigations of the colonies of western gulls on Santa Barbara Island, California, have revealed a surplus of females and the occurrence of female-female pairs that produce clutches with as many as six eggs. Females are able to establish and defend breeding territories, behaviours generally thought to be under the control of androgens. There are very few significant differences in circulating levels of the luteinizing hormone and androgens among breeding males, breeding females in heterosexual pairs, and breeding females in homosexual pairs. In contrast, however, only females sampled in 1877, in both homo- and heterosexual pairs, have elevated plasma levels of oestrogens, in spring, coincident with the period in which they show courtship behaviours such as food begging and solicitation of copulation. Given a sex ratio skewed in favour of females, as is apparently the case with the colonies of this species on Santa Barbara Island, and the essentially equal plasma levels of androgens in males and females, it is not difficult to rationalize the formation of female-female pairs. Our findings do not support the hypothesis that female-female pairing involves hormonal masculinization of one member of the pair. © 1982.

The southeastern Bering Sea is characterized by three mixing regimes, separated by fronts associated with the 50, 100, and 200 m isobaths. Phytoplankton to zooplankton transfer-rates are high in waters over the outer shelf and slope (seaward of the 100 m front) relative to transfer in waters over the middle shelf (between the 50 and 100 m fronts). To see whether this difference is reflected at a higher trophic level, we computed carbon flux to the 11 commonest seabird species. Bird-density data (for the period 1975 through 1979) were combined with daily caloric requirement, which is an allometric function of body size in this endothermic group. Minimum transfer to seabirds over a 153 d period (April-August) was 30 mg C m-2 for the middle shelf and 48 mg C m-2 for outer shelf and slope waters. Trophic transfer to subsurface-feeding birds (shearwaters, murres and auklets) differed little between regions. In contrast, trophic transfer to surface-feeding birds (fulmars, petrels, and kittiwakes) in the outer shelf and slope waters was 3 times greater than in the waters of the middle shelf. Thus, for seabirds as a whole, pathways of energy transfer differed more between regions than did total carbon flux. © 1982 Springer-Verlag.

A survey of museum specimens revealed large interspecific variability in the sex ratio in 14 species [Mew, ring-billed, laughing, Franklin's, Bonaparte's, Heerman's, California, herring, Thayer's, western, glaucous, glaucous-winged, and great black-backed gulls, and blacklegged kittiwake] of North American gulls. In the three black-headed species, (Larus atricilla, L. pipixcan, and L. philadelphia), females outnumbered males among prefledglings, but males outnumbered females among adults. In the white-headed gulls, the male/female ratio in prefledglings did not vary significantly from 1.0 in any species. However, among first-year birds, females outnumbered males in 8 white-headed species. Among adults, the male/female ratio was < 1.0 in the Mew and Ring-billed gulls, > 1.0 in the Great Black-backed Gull, and = 1.0 in the other white-headed gulls.

Average clutch size for large Larus gulls is close tothree eggs, and the production of a clutch of four is uncommon (Keith 1966; Paludan 1951; Vermeer1963). We report here on a colony of Western Gulls(Larms occidentalis) in which many clutches containingfour and five eggs were found. It is of particularinterest that in these large clutches not only washatching success low but also eggshell thickness wasreduced.

With the study of the equilibrium theory ofisland biogeography pioneered by MacArthurand Wilson ( 1963, 1967), increasing attention has been paid to the study of turnover rates (Mayr 1965; Diamond 1969, 1971; Power1972; Terborgh and Faaberg 1973). Thefailure of bird species turnover rates to showthe predicted negative correlation with islandsize in the California Channel Islands (Diamond1969) raises questions as to what factorsother than island size may be involved indetermining species turnover. · Previous studiesof avifaunal turnover have treated faunas asa whole and have not differentiated turnoverrates for rare species from those of commonspecies. Since very large birds and speciesat high levels on the food chain often existat relatively low densities, these organismswould be expected to have a greater probabilityof extinction on small islands than thosespecies which maintain larger populations(Brown 1971). A theoretical basis for thishypothesis can be derived from Gilpin ( 197 4).He has shown ( pers. comm.) that extinctionrates should be a negative exponential functionof K, and thus should be very sensitiveto small population size.

Pairs of females that remain together from one year to the next are associated with the presence of supernormal clutches in western gull nests. Intervals between laying of eggs in supernormal clutches are less than those found in normal clutches, a result indicating both females in a pair contribute to the clutch. Most eggs in supernormal clutches are infertile. The pairs of females occupy territories that are not shared with a resident male. In three homosexual pairs one of the females exhibited behaviors normally ascribed only to males.

Typically, red-legged kittiwakes used ledges 1 dm deep; northern fulmars, black-legged kittiwakes, and thick-billed murres used ledges of an intermediate 2-4 dm depth; red-faced cormorants used ledges 3-6 dm deep; and common murres occurred singly on shallow ledges or in groups on deeper ledges. Fulmars and murres, which did not build nests, used nearly horizontal ledges exclusively; the nest-building species occurred on a wider range of slopes. Only red-legged kittiwake regularly used ledges with over 50% cover by overhanging cliff within 5 dm of the ledge. Classification of the measured ledges of the cormorant, the 2 kittiwakes, and thick- billed murre by a discriminant function analysis revealed significantly greater overlap than expected between the species pairs of cormorant with thick-billed murre, black-legged with red-legged kittiwake, and black-legged kittiwake with thick-billed murre.-from Authors

Tested the hypothesis that female-female pairings in ring-billed Larus delawarensis and California gulls L. californicus result from a shortage of males in the breeding population, by removing males from one ring-billed and 4 California gull colonies early in the breeding season. The frequency of 4-6 clutches, used as an index of female-female pairings, was significantly higher in these colonies than in nearby control colonies, supporting the hypothesis. Female-female pairings allow females the chance to breed when they are unable to obtain a male partner. -from Authors

Synthliboramphus hypoleucus were studied on Santa Barbara Island, California. Clutch initiation occurred from March-June and usually peaked in April. The 2-egg clutch was 45% of the female's weight. Eggs were laid eight days apart. Both sexes shared duties during a 34-day incubation period; partners relieved one another every 3-4 days. Eggs were typically left unattended in the interval between laying of successive eggs, immediately after clutch completion, and sporadically during incubation. Breeders and non-breeders of both sexes followed similar patterns of weight change, reflecting similar patterns of colony attendance; murrelets lost weight after the egg-laying period, then gradually gained weight through the rest of the breeding season. The downy young left the nest two nights after hatching, unfed and weighing

Compared reproductive performance of 5 species of seabirds at St. George Island (2.5 million birds) and St. Paul Island (250 000 birds), in the SE Bering Sea. All species had lower chick growth rates at the larger colony; differences were statistically significant in 4 species. Fledge weights of common murres Uria aalge on St. George Island were 84-88% of those on St. Paul. Average fledge weights of thick-billed murres U. lomvia on St. George were only 74% of those for chicks from St. Paul. No significant differences were found in clutch size or breeding success between populations breeding at the 2 colonies. For black-legged kittiwakes Rissa tridactyla common murres, and thick-billed murres, analysis was extended to include published data from other colonies. There were consistently negative relationships between population size and several measures of breeding performance (clutch size, growth rate, fledge weight, and breeding success). In addition to the lower breeding success at colonies that support large populations, chicks from these colonies may be subject to higher postfledging mortality because of fledging at lower weights.-from Authors

Rissa tridactyla were studied on St. Paul Island, Alaska. In 2-egg clutches, 1st-laid eggs were largest; they were incubated before 2nd eggs were laid and consequently hatched first. Chicks from 1st-laid eggs begged more frequently, fed more frequently, grew faster, and were more aggressive than their sibs. These sibling differences frequently facilitated the ejection of younger siblings from the nest by 1st-hatched young. Lower feeding and growth rates and higher aggression levels occurred in broods in which the 2nd chicks subsequently died than in broods in which both chicks fledged. Chick loss was most frequent during inclement weather. Data are consistent with the hypothesis that brood reduction is related to amount of food that chicks receive.-from Authors

Applications of the model to populations of Brunnich's guillemot Uria lomvia, common guillemot U. aalge, red-legged kittiwake Rissa brevirostris, and black-legged kittiwake R. tridactyla breeding on the Pribilof Islands suggest that guillemot mortality is greatest following perturbations located in shallow inshore areas about the breeding islands, while kittiwakes are less severely affected by localized perturbations but are sensitive to spills occurring over a wider area about the islands. Model explorations employing chronic low-level pollution rather than one-time perturbations suggest that the guillemot population breeding on St. George Island could tolerate an overall reduction of 10% in the food supply without suffering a major decline in fledging success, but a reduction of 40% would lead to total reproductive failure in the colony. The effects of one-time mortality on guillemots are much more severe if adults rather than first-year birds suffer the mortality. If a given level of one-time mortality is superimposed on a chronic low-level change in survivorship or fecundity, recovery times are markedly longer.-from Authors

It has been hypothesized that differentiation in food web structure occurs across the Bering Sea continental shelf as a result of seasonal differentiation of water masses. We tested this idea using an apex predator, pelagic birds. Seasonal abundance of birds in central Bristol Bay was estimated from counts made while underway between hydrographic stations. Prey and body mass were determined from birds collected at sea. Daily intake was estimated as an allometric function of body mass. Annual occupancy was estimated as the integral of a normal curve fit to seasonal data. Estimated carbon flux to seabirds in the middle domain was 0.12 gC m-2 y-1 in 1980, 0.18 gC m-2 y-1 in 1981. Carbon flux to seabirds in the adjacent waters of the outer shelf domain was 1.8 times higher than in the middle domain in 1980, 1.6 times higher in 1981. Carbon flux to seabirds in the inner domain was 1.2 times higher than in the middle domain in 1980, and 3.3 times higher in 1981. Carbon flux to seabirds in the outer domain was due primarily to non-diving species, principally northern fulmars (Fulmarus glacialis) during the summer and autumn, and Larus gulls in the autumn and winter. Flux to seabirds in the inner domain was due to diving birds, principally murres (Uria sp.) in the spring and shearwaters (Puffinus sp.) during the summer. The euphausiid Thysanoessa raschii was the primary food source of shearwaters in shallow waters of the inner shelf domain. A more diverse set of prey, including squid, jellyfish, hyperiids, and fish, was taken by shearwaters and fulmars in the deeper waters of the outer and middle shelf domains. This result suggests that prey diversity is higher in seasonally stratified waters of outer Bristol Bay than in mixed waters of inner Bristol Bay. Greater energy flux to diving species in shallow water, and greater energy flux to non-divers in deep water may be a function of topographic control of prey patchiness. © 1985.

Located on the extensive continental shelf of the Bering Sea, the Pribilof Islands, Alaska are the site of one of the largest breeding colonies of seabirds in the northern hemisphere. During summer these islands are surrounded by a front that separates vertically homogeneous waters from well stratified waters farther seaward. We studied the front with hydrographic data and the bird distributions with concurrent counts during summer 1977 and spring, summer and fall 1978. Murres (Uria lomvia and U. aalge) sitting on the water aggregated near the front during summer 1977 and probably during summer 1978. Other species, such as northern fulmars (Fulmarus glacialis) and auklets (Aethia pusilla and A. cristatella) were unaffected by the front. We hypothesize that the aggregation of the murres was related to an enhanced availability of their food near the front. © 1983.

Topographically-induced flow gradients can concentrate seabird prey in several different ways, and are potentially important to marine birds in shelf ecosystems such as the south-eastern Bering Sea. We tested the hypothesis that attendance by seabirds was greater at fronts maintained by strong surface flow gradients than at fronts maintained by weak or intermittent surface flow gradients. An analysis of 62 crossings of flow gradients identified from temperature and salinity gradients showed that local increase in attendance was greater in areas of strong surface flow gradient than in an area of weak surface flow gradients. Attendance by marine birds depended on the strength of a flow gradient rather than on the presence or absence of a front. © 1987.