Fratercula Cirrhata Research Articles

Parental Provisioning and Nestling Departure Decisions: A Supplementary Feeding Experiment in Tufted Puffins (Fratercula cirrhata) on Triangle Island, British Columbia

Parental Provisioning and Nestling Departure Decisions: A Supplementary Feeding Experiment in Tufted Puffins (Fratercula cirrhata) on Triangle Island, British Columbia

Parental Provisioning and Nestling Departure Decisions: A Supplementary Feeding Experiment in Tufted Puffins (Fratercula Cirrhata) on Triangle Island, British Columbia

Abstract I used a supplemental feeding experiment to determine whether adult Tufted Puffins (Fratercula cirrhata) would decrease provisioning effort in response to a reduction in nestling nutritional requirements, and to investigate the relationship between parental provisioning effort and timing of fledging. As predicted, parents of the supplemented nestlings decreased the number of provisioning trips but did not alter bill-load size or prey composition. Supplemental feeding significantly increased the growth of the culmen and tarsus but had no detectable effect on wing growth or body mass of chicks. Supplemented nestlings fledged significantly older than control nestlings. The maximum mass attained by the nestling and the age at which mass peaked also influenced timing of fledging. These results demonstrate that fledging age is influenced by both the energy provided by the parents and the nestling's developmental state and are consistent with the hypothesis that nestlings time their departure from the nest based on the costs and benefits of remaining.

Polymorphic Flight-Feather Molt Sequence in Tufted Puffins (Fratercula Cirrhata): A Rare Phenomenon in Birds

Abstract Previous reports have stated that Tufted Puffins (Fratercula cirrhata) lose all of their flight feathers simultaneously (or nearly so) during flight-feather molt and replace them in no apparent order. In contrast, we found that captive second-year (SY) Tufted Puffins (1) typically require 15 and 10 days to lose their primaries and secondaries, respectively, during their first flight-feather molt, and an average of 21 days to lose all of their remiges; and (2) replace their primaries in either of two discrete sequences. In 9 of 13 birds, primary molt began at the innermost primary, P1, and progressed distally to the outermost functional primary, P10. However, in the remaining four birds, primary molt began in the middle of the primaries (P5-P7) and progressed both distally to P10 and proximally toward P1. Before the proximal wave reached P1, a second wave of molt was initiated at P1 and progressed distally, typically replacing P2 and P3 before reaching the proximal wave. Such polymorphism in flight-feather molt sequence is rare in birds, having been reported previously only in a few passerine species. Secondary molt began about 13 days after onset of primary molt and finished at about the same time as primary molt, resulting in a total duration of flight-feather molt of ∼54 days and a flightless period of ∼40 days.

POLYMORPHIC FLIGHT-FEATHER MOLT SEQUENCE IN TUFTED PUFFINS (FRATERCULA CIRRHATA): A RARE PHENOMENON IN BIRDS

Abstract Previous reports have stated that Tufted Puffins (Fratercula cirrhata) lose all of their flight feathers simultaneously (or nearly so) during flight-feather molt and replace them in no apparent order. In contrast, we found that captive second-year (SY) Tufted Puffins (1) typically require 15 and 10 days to lose their primaries and secondaries, respectively, during their first flight-feather molt, and an average of 21 days to lose all of their remiges; and (2) replace their primaries in either of two discrete sequences. In 9 of 13 birds, primary molt began at the innermost primary, P1, and progressed distally to the outermost functional primary, P10. However, in the remaining four birds, primary molt began in the middle of the primaries (P5-P7) and progressed both distally to P10 and proximally toward P1. Before the proximal wave reached P1, a second wave of molt was initiated at P1 and progressed distally, typically replacing P2 and P3 before reaching the proximal wave. Such polymorphism in fligh...

PARENTAL PROVISIONING AND NESTLING DEPARTURE DECISIONS: A SUPPLEMENTARY FEEDING EXPERIMENT IN TUFTED PUFFINS (FRATERCULA CIRRHATA) ON TRIANGLE ISLAND, BRITISH COLUMBIA

Abstract I used a supplemental feeding experiment to determine whether adult Tufted Puffins (Fratercula cirrhata) would decrease provisioning effort in response to a reduction in nestling nutritional requirements, and to investigate the relationship between parental provisioning effort and timing of fledging. As predicted, parents of the supplemented nestlings decreased the number of provisioning trips but did not alter bill-load size or prey composition. Supplemental feeding significantly increased the growth of the culmen and tarsus but had no detectable effect on wing growth or body mass of chicks. Supplemented nestlings fledged significantly older than control nestlings. The maximum mass attained by the nestling and the age at which mass peaked also influenced timing of fledging. These results demonstrate that fledging age is influenced by both the energy provided by the parents and the nestling's developmental state and are consistent with the hypothesis that nestlings time their departure from the n...

Tufted puffin reproduction reveals ocean climate variability.

Anomalously warm sea-surface temperatures (SSTs) are associated with interannual and decadal variability as well as with long-term climate changes indicative of global warming. Such oscillations could precipitate changes in a variety of oceanic processes to affect marine species worldwide. As global temperatures continue to rise, it will be critically important to be able to predict the effects of such changes on species' abundance, distribution, and ecological relationships so as to identify vulnerable populations. Off the coast of British Columbia, warm SSTs have persisted through the last two decades. Based on 16 years of reproductive data collected between 1975 and 2002, we show that the extreme variation in reproductive performance exhibited by tufted puffins (Fratercula cirrhata) was related to changes in SST both within and among seasons. Especially warm SSTs corresponded with drastically decreased growth rates and fledging success of puffin nestlings. Puffins may partially compensate for within-season changes associated with SST by adjusting their breeding phenology, yet our data also suggest that they are highly vulnerable to the effects of climate change at this site and may serve as a valuable indicator of biological change in the North Pacific. Further and prolonged increases in ocean temperature could make Triangle Island, which contains the largest tufted puffin colony in Canada, unsuitable as a breeding site for this species.

The State of Food Resources and Reproductive Success of Tufted and Horned Puffins in the Northern Sea of Okhotsk

Studies on the reproductive biology of seabirds on Talan and Umara islands in 1987–1999 showed that the diet of nestlings and reproductive success of the tufted puffin (Lunda cirrhata) and horned puffin (Fratercula corniculata) considerably varied in different colonies. This was determined by differences in the hydrologic characteristics of water areas and the state of food resources in Taui Bay (the northern Sea of Okhotsk). The reproductive success of tufted puffins was higher on Umara Island due to more favorable environmental conditions and relatively stable food resources in Odyan Bay. The parameters of reproductive success and the nestling diet in tufted and horned puffins from Talan Island differed considerably. The survival of nestlings was always higher in horned puffins, which was related to some characteristics of their feeding ecology.

Status of Seabirds Breeding in Hokkaido.

The historic and present status of seabirds in Hokkaido is summarized, based on published and unpublished data. At least 12 species breed in Hokkaido. The breeding pairs of seabirds in recent years in Hokkaido are estimated as follows: Common Murre (Uria aalge) <10; Tufted Puffin (Lunda cirrhata) 15; Spectacled Guillemot (Cepphus carbo) 100; Ancient Murrelet (Synthliboramphus antiquus) <20; Rhinoceros Auklet (Cerorhinca monocerata) 300, 000; Slaty-backed Gull (Larus schistisagus) 10, 000; Black-tailed Gull (Larus crassirostris) 30, 000; Red-faced Cormorant (Phalacrocorax urile) 25; Japanese Cormorant (Phalacrocorax capillatus) 3, 000; Pelagic Cormorant (Phalacrocorax pelagicus) 10; Streaked Shearwater (Calonectris leucomelas) 120; Leach's Stormpetrel (Oceanodroma leucorhoa) 900, 000. The present status of the Long-billed Murrelet (Brachyramphus perdix) is unclear. The colony size of Common Murre shrank with annual decreasing rate of 12.2% (1938-80)-26.6% (1981-94) on Teuri Island. It has decreased 24.8% annually, and it has not been observed on Moyururi Island since 1985. The Tufted Puffin and Spectacled Guillemot decreased 9-15% annually during the last 30 years. The Slaty-backed Gull increased 11.0% annually (1963-95) on Teuri Island, and 8.5% annually (1972-93) on Yururi Island. Black-tailed Gull increased by 5% annually (1987-2000) on Rishiri Island, but decreased on Teuri Island during the 1990's. The Japanese Cormorants increased by 5-9% annually on Teuri and Yururi Islands. Its number increased at annual rate of 6.4% during 1959-86, but decreased at annual rate of 10.4% during 1987-96 on Moyururi Island. At 12 of the 14 surveyed colonies predation by gulls and/or crows were reported, and disturbances caused by introduced rats and cats was reported at five colonies. Although most of the colonies are legally protected, few conservation programs have been effectively conducted. Seabird mortality by fishing nets was reported around six colonies, but protective measure for seabirds has not been taken. We here propose, therefore, non-fishing sea areas for seabird protection around such breeding islands.

Does Kleptoparasitism by Glaucous-Winged Gulls Limit the Reproductive Success of Tufted Puffins?

AbstractInterspecific kleptoparasitism (food stealing) occurs in many seabird species and can sometimes significantly affect host individuals and populations. We investigated effects of kleptoparasitism by Glaucous-winged Gulls (Larus glaucescens) on a population of Tufted Puffins (Fratercula cirrhata) in which almost all chicks die before fledging in some years. Rates of kleptoparasitism were estimated during two seasons and compared with several spatial and temporal factors that have been predicted to influence kleptoparasitism rates both within and among seasons. Kleptoparasitism rates increased from 2% in the first year to 19% in the second, whereas puffin fledging success declined precipitously from 81% in the first year to 11% in the second. Within years, kleptoparasitism rates increased with number of puffins returning with fish, decreased during fair weather, and were unaffected by tidal height. Spatially, those rates increased with puffin burrow density and declined with angle of the nesting slope. Gull kleptoparasitism success increased during foul weather and at higher puffin nesting elevations. Despite those associations, survival of puffin chicks was not influenced by kleptoparasitism activity near their nests although it increased with a combination of low elevation and high slope at the nesting burrow. Neither kleptoparasitism nor predation by gulls were exceptional relative to other seabird colonies and they were unlikely to cause reproductive failures that characterize puffins at that site. Other factors, particularly food shortages at sea, merit further attention in explaining those failures.

DOES KLEPTOPARASITISM BY GLAUCOUS-WINGED GULLS LIMIT THE REPRODUCTIVE SUCCESS OF TUFTED PUFFINS?

Abstract Interspecific kleptoparasitism (food stealing) occurs in many seabird species and can sometimes significantly affect host individuals and populations. We investigated effects of kleptoparasitism by Glaucous-winged Gulls (Larus glaucescens) on a population of Tufted Puffins (Fratercula cirrhata) in which almost all chicks die before fledging in some years. Rates of kleptoparasitism were estimated during two seasons and compared with several spatial and temporal factors that have been predicted to influence kleptoparasitism rates both within and among seasons. Kleptoparasitism rates increased from 2% in the first year to 19% in the second, whereas puffin fledging success declined precipitously from 81% in the first year to 11% in the second. Within years, kleptoparasitism rates increased with number of puffins returning with fish, decreased during fair weather, and were unaffected by tidal height. Spatially, those rates increased with puffin burrow density and declined with angle of the nesting slo...

Climate change causes contrasting trends in reproductive performance of planktivorous and piscivorous alcids

Summary 1. Eight years of observations on seabird reproductive success and oceanographic change in Tauyskaya Bay (Okhotsk Sea, north‐western Pacific) were used to evaluate the hypothesis that interannual climate change causes opposite trends in reproductive performances of planktivorous auklets (Aethia cristatella and Cyclorhinchus psittacula) vs. piscivorous puffins (Lunda cirrhata and Fratercula corniculata). 2. The climate change was assessed by examining changes in sea‐surface temperature (SST), time of permanent ice disappearance (ID), wind (WV) and current vectors (CV). Changes in the distribution of zooplankton biomass in the study region were used to assess changes in prey communities. Bird reproductive success was determined as the number of chicks fledged per nest occupied. 3. There were two distinct sets of oceanographic conditions in the study region, as reflected in the SST, ID, WV and CV. Strong northerly winds in the spring produced a late ice disappearance in the study region, whereas easterly winds determined an early ice disappearance. The patterns in ice disappearance were significantly correlated with SST anomalies during the summer. A negative SST anomaly (– 1·2 °C) defined a ‘cold’ regime, whereas a positive SST anomaly ( + 1·2 °C) defined a ‘warm’ regime. 4. Reproductive success of planktivorous auklets was negatively correlated with the SST in the western part of Tauyskaya Bay, whereas reproductive success of piscivorous puffins was positively correlated with the SST. The ‘cold’ season in 1988 was characterized by a strong in‐flow of water masses into the bay area. The ‘warm’ season in 1989 was characterized by well‐mixed warm water inside the bay that were separated from colder water masses outside the bay. Macro‐zooplankton, which were the main prey of planktivorous auklets, were more abundant during the ‘cold’ regime of the ecosystem. Meso‐zooplankton, a potential prey of juvenile pelagic fish, were more abundant during the ‘warm’ regime of the ecosystem. 5. Interannual oceanographic change probably impacts alcid reproductive performances by affecting food accessibility to planktivorous auklets and piscivorous puffins in opposite ways.

Seasonal Movements and Pelagic Habitat Use of Murres and Puffins Determined by Satellite Telemetry

AbstractWe tracked the movements of Common Murres (Uria aalge), Thick-billed Murres (U. lomvia), and Tufted Puffins (Fratercula cirrhata) using surgically implanted satellite transmitters. From 1994–1996, we tagged 53 birds from two colonies in the Gulf of Alaska (Middleton Island and Barren Islands) and two colonies in the Chukchi Sea (Cape Thompson and Cape Lisburne). Murres and puffins ranged 100 km or farther from all colonies in summer, but most instrumented birds had abandoned breeding attempts and their movements likely differed from those of actively breeding birds. However, murres whose movements in the breeding period suggested they still had chicks to feed foraged repeatedly at distances of 50–80 km from the Chukchi colonies in 1995. We detected no differences in the foraging patterns of males and females during the breeding season, nor between Thick-billed and Common Murres from mixed colonies. Upon chick departure from the northern colonies, male murres—some believed to be tending their flightless young—drifted with prevailing currents toward Siberia, whereas most females flew directly south toward the Bering Sea. Murres from Cape Thompson and Cape Lisburne shared a common wintering area in the southeastern Bering Sea in 1995, and birds from Cape Lisburne returned to the same area in the winter of 1996. We conclude that differences in foraging conditions during summer rather than differential mortality rates in winter account for contrasting population trends previously documented in those two colonies.

SEASONAL MOVEMENTS AND PELAGIC HABITAT USE OF MURRES AND PUFFINS DETERMINED BY SATELLITE TELEMETRY

We tracked the movements of Common Murres (Uria aalge), Thick-billed Murres (U. lomvia), and Tufted Puffins (Fratercula cirrhata) using surgically implanted satellite transmitters. From 1994–1996, we tagged 53 birds from two colonies in the Gulf of Alaska (Middleton Island and Barren Islands) and two colonies in the Chukchi Sea (Cape Thompson and Cape Lisburne). Murres and puffins ranged 100 km or farther from all colonies in summer, but most instrumented birds had abandoned breeding attempts and their movements likely differed from those of actively breeding birds. However, murres whose movements in the breeding period suggested they still had chicks to feed foraged repeatedly at distances of 50–80 km from the Chukchi colonies in 1995. We detected no differences in the foraging patterns of males and females during the breeding season, nor between Thick-billed and Common Murres from mixed colonies. Upon chick departure from the northern colonies, male murres—some believed to be tending their flightless young—drifted with prevailing currents toward Siberia, whereas most females flew directly south toward the Bering Sea. Murres from Cape Thompson and Cape Lisburne shared a common wintering area in the southeastern Bering Sea in 1995, and birds from Cape Lisburne returned to the same area in the winter of 1996. We conclude that differences in foraging conditions during summer rather than differential mortality rates in winter account for contrasting population trends previously documented in those two colonies.

Metabolic and developmental responses of alcid chicks to experimental variation in food intake.

I tested whether the ability of chicks to suspend growth and developmental processes in response to food shortages is greater among alcids with food resources that fluctuate over short time periods than it is among close relatives with food that is continuously available. I examined changes in chick resting metabolic rate (RMR) in response to short-term food deprivation in horned and tufted puffins (intermittent food provisioning) and crested and parakeet auklets (continuous food provisioning). RMR was based on measurements of chick oxygen consumption rates (Vo2) under thermoneutral conditions. RMR of postabsorptive chicks scaled allometrically with body mass, and regression slopes were statistically indistinguishable among species. Mass-independent RMR of the same individuals decreased significantly after 48 h of food deprivation. The decrease in the mass-independent RMR was greater in puffins (46.8% in horned and 47.4% in tufted puffins) than in auklets (29.4% in crested and 23.7% in parakeet auklets). To test whether the observed decrease in RMR was due to less energy being allocated to growth, I examined developmental responses of horned and tufted puffins to experimental variation in rates of food intake. I found retarded growth rates in body mass, skeletal elements, and feathers in chicks experiencing low rates of food intake. The retardation of growth processes extended the developmental period. My findings suggest that developmental plasticity in juvenile alcids might be related to temporal variability of prey in oceanic environments.

Declines in Marine Bird Populations in Prince William Sound, Alaska Coincident with a Climatic Regime Shift

-Analyses of marine bird surveys conducted in Prince William Sound, Alaska in July 1972 were compared to surveys in July 1989, 1990, 1991, and 1993 and indicated that populations of several taxa of marine birds that prey on fish have declined in Prince William Sound, but most taxa that feed on other prey species, such as benthic invertebrates, have not declined. Red-throated Loon (Gavia stellata), Pacific Loon (G. pacifica), cormorant (Phalacrocorax spp.), Surf Scoter (Melanitta perspicillata), Bonaparte's Gull (Larus philadelphia), terns (Sterna spp.), Pigeon Guillemot (Cepphus columba), Brachyramphus murrelets (Brachyramphus marmoratus and B. brevirostris), Parakeet Auklet (Cyclorrhynchus psittacula), Tufted Puffin (Fratercula cirrhata), and Horned Puffin (Fratercula corniculata) populations declined by >50%. Most of these are piscivores, feeding on schooling fish. Some non-piscivorous taxa, such as Harlequin Ducks (Histrionicus histrionicus), goldeneyes (Bucephala clangula and islandica), and Black Oystercatchers (Haematopus bachmani), have increased in Prince William Sound between 1972 and 1989-1993, although a portion of the population was killed by the T/VExxon Valdez oil spill. Declines in piscivorous bird populations also have been documented in the Gulf of Alaska, the Bering Sea, and along the California coast in the past two decades and have been coincidental to changes in forage fish species in the North Pacific Ocean. Many of the declines appear to be related to changes in forage fish abundance that occurred during a climatic regime shift in the north Pacific Ocean, although some taxa were also affected by the Exxon Valdez oil spill. Received 11 November 1998, accepted 6January 1999.

Selection of Forage-Fish Schools by Murrelets and Tufted Puffins in Prince William Sound, Alaska

We collected hydroacoustic and bird-observation data simultaneously along transects in three areas in Prince William Sound, Alaska, 21 July-11 August 1995. The probability of the association of fish schools with Marbled Murrelets (Brachyramphus mar-moratus) and Tufted Puffins (Fratercula cirrhata) was determined through the use of resource selection functions based on logistic regression. Mean (± SD) group sizes were small for both species, 1.7 ± 1.1 and 1.2 ± 0.7 for Marbled Murrelets and Tufted Puffins, respectively. Oceanographically, all study areas were stratified with synchronous thermo- and pycnoclines (a water layer of increasing temperature and density. respectively, with increasing depth). Our analysis indicated that Tufted Puffins selected fish schools near their colony, whereas Marbled Murrelets selected smaller, denser fish schools in shallower habitats. We suggest that murrelets selected shallower habitats in response to lower maximum diving depths than puffins. Small feeding-groups size is discussed in terms of foraging theory and as a consequence of dispersed, low density food resources.

Descriptions of Larval Contracaecum variegatum (Rudolphi, 1809) and Adult Contracaecum sp. (Nematoda: Anisakidae) Collected from Seabirds of the Bering Sea.

Third- and fourth-stage larvae of Contracaecum variegatum (Rudolphi, 1809) are described from specimens collected from the stomachs of the Thick-billed Murre (Uria lomvia), Common Murre (U. aalge), and Tufted Puffin (Lunda cirrhata) from the Bering Sea. The Tufted Puffin is a new definitive host for C. variegatum. Almost all of the seabirds examined were infected with a relatively high intensity with C. variegatum. It would therefore appear that this parasite is a very common and abundant nematode of seabirds in the Bering Sea. Contracaecum yamaguti (Mawson, 1956) is considered a junior synonym of C. variegatum. An adult of Contracaecum sp. with an aberrant ventricular appendix is described based on one fragment of a specimen from the stomach of the Common Murre.

Habitat Use, Diet and Breeding Biology of Tufted Puffins in Prince William Sound, Alaska

Habitat use, diet and breeding biology of tufted puffins (Fratercula cirrhata) were studied in Prince William Sound, Alaska, during summer 1995. On Seal Island, 112 puffin bur- rows (71% active) were located. Of 95 accessible burrows, 49% were typical earthen burrows, whereas the remainder were atypical for the species (e.g., under tree roots). Hatching success ('79%), fledging success (282%), chick growth rates (17.7 g/day), asymptotic (600 g) and fledg- ing (563 g) weights, meal sizes (14.2 g), meal delivery rates (5.32 meals/day), and daily rations (75.5 g/day) were all average or above-average for tufted puffins in Alaska. A total of 42 chick meals, comprising 125 individual prey were collected. Meals were composed of juvenile pollock (12.7% of total mass), herring (21.8%), prowfish (32.3%), salmonids (24.1%), and capelin, sand- lance and squid (<5% each). Tufted puffin populations in Prince William Sound are relatively small, and may be limited by low densities of prey in the Sound, nest-site availability, and heavy rainfall.

Climatic and Oceanographic Influences on Island Use in Four Burrow-Nesting Alcids

More than 2,000,000 pairs of burrow-nesting alcids breed along the Pacific coast of North America between 480 and 550 N latitude. Most occur in a few large colonies leaving >98% of coastal islands unoccupied. There is considerable local variation in climate and oceanographic conditions, but such variation is in part predictable since it is largely attributable to regional orographic conditions and stable seasonal weather patterns. Here we examine colony-site location in four burrow-nesting alcids, Ancient Murrelet Synthliboramphus antiquus, Cassin's Ptychoramphus aleuticus, and Rhinoceros Auklet Cerorhinca monocerata and Tufted Puffin Fratercula cirrhata, with respect to variation in climate and oceanographic conditions. Colonies are located on islands in colder, more saline water, and are subject to less intense rainfall than non-colony sites. Drier nesting sites offer several potential advantages including reduced burrow erosion, low risk of flooding, and easier maintenance of burrow microclimate. Cold, saline water is associated with increased food availability while freshwater runoff is associated with decreased marine productivity.

Influence of pycnocline topography and water-column structure on marine distributions of alcids (Aves: Alcidae) in Anadyr Strait, Northern Bering Sea, Alaska

Systematic ship-board surveys were used to simultaneously record seabird abundances and resolve coarse-scale (3 to 10 km) horizontal and fine-scale (1 to 10 m) vertical variability in water-column structure and bathymetry for portions of the coastal zone in Anadyr Strait near western St. Lawrence Island, northern Bering Sea, Alaska, during August and September 1987. Three plankton-feeding alcids, parakeet (Cyclorrhynchus psittacula), crested (Aethia cristatella) and least (A. pusilla) auklets, each exhibited distinct associations for different pycnocline characteristics. Least auklets were more abundant in mixed water, but they also occurred within stratified water where the pycnocline and upper-mixed layer were shallow (≤8 m) and thin (≤10 m), respectively. Low body mass (85 g), high buoyancy, and relatively poor diving ability may have restricted this auklet to areas where water-column strata nearly intersected the surface, or to areas from which strata were absent altogether due to strong vertical mixing. Parakeet and crested auklets, which are larger-bodied (ca. 260 g) planktivores with presumably greater diving ability, were more abundant in stratified water, and both species exhibited less specific affinities for water-column characteristic at intermediate and shallow levels. All three auklets avoided locations with strong pycnocline gradients (≤0.22σ t m−1), a crude index of the strong, subsurface shear in water velocities characteristic of this region. Auklet distributions in Anadyr Strait were consistent with: (1) strata accessibility, as estimated from relationships between body mass and relative diving ability, (2) possible avoidance of strong subsurface water motions, and (3) habits and distributions of plankton prey. In contrast, largebodied (>450 g) alcids [i.e., common (Uria aalge) and thick-billed (U. lomvia) murres, pigeon guillemots (Cephus columba), tufted (Fratercula cirrhata), and horned (F. corniculata) puffins feeding on fish or benthic invertebrates] showed no consistent relationships with either the pycnocline or upper-mixed layers. All large alcids were more common in stratified than in vertically-mixed waters, but differences in abundance between mixing regimes were small or equivocal. The only measured variable with which all large alcids were associated was total water-column depth: murres, guillemots, and puffins each used areas with shallow sea floors and avoided areas with deeper sea floors. Failure of large alcids to discriminate among foraging areas in Anadyr Strait as a function of pycnocline topography and strength may be attributable to: (1) greater reliance on large pelagic and benthic prey not associated with the pycnocline; (2) higher body mass, lower buoyancy, and greater diving ability; (3) foraging over a uniquely shallow continental shelf where all vertical strata, including the sea floor, are potentially accessible from the ocean surface.