Foraging segregation of two congeneric diving seabird species breeding on  St. George Island, Bering Sea

Abstract. Subarctic environmental changes are expected to affect the foraging ecology of marine top predators, but the response to such changes may vary among species if they use food resources differently. We examined the characteristics of foraging behavior of two sympatric congeneric diving seabird: common (Uria aalge: hereafter COMUs) and thick-billed (U. lomvia: hereafter TBMUs) murres breeding on St. George Island, located in the seasonal sea-ice region of the Bering Sea. We investigated their foraging trip and flight durations, diel patterns of dive depth, and underwater wing strokes, along with wing morphology and blood stable isotope signatures and stress hormones. Acceleration–temperature–depth loggers were attached to chick-guarding birds, and data were obtained from 7 COMUs and 12 TBMUs. Both species showed similar mean trip duration (13.2 h for COMUs and 10.5 h for TBMUs) and similar diurnal patterns of diving (frequent dives to various depths in the daytime and less frequent dives to shallow depths in the nighttime). During the daytime, the dive depths of COMUs had two peaks in shallow (18.1 m) and deep (74.2 m) depths, while those of TBMUs were 20.2 m and 59.7 m. COMUs showed more frequent wing strokes during the bottom phase of dives (1.90 s−1) than TBMUs (1.66 s−1). Fish occurred more frequently in the bill loads of COMUs (85 %) than those of TBMUs (56 %). The δ15N value of blood was significantly higher in COMUs (14.5 ‰) than in TBMUs (13.1 ‰). The relatively small wing area (0.053 m2) of COMUs compared to TBMUs (0.067 m2) may facilitate their increased agility while foraging and allow them to capture more mobile prey such as larger fishes that inhabit deeper depths. These differences in food resource use may lead to the differential responses of the two murre species to marine environmental changes in the Bering Sea.

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Foraging segregation of two congeneric diving seabird species (common and thick-billed murres) breeding on St. George Island, Bering Sea

Biogeosciences Discussions ◽

10.5194/bgd-12-18151-2015 ◽

2015 ◽

Vol 12 (21) ◽

pp. 18151-18183 ◽

Cited By ~ 3

Author(s):

N. Kokubun ◽

T Yamamoto ◽

N. Sato ◽

Y. Watanuki ◽

A. Will ◽

...

Keyword(s):

Foraging Behavior ◽

Bering Sea ◽

Environmental Changes ◽

Dive Depth ◽

Bottom Phase ◽

Flight Duration ◽

Seabird Species ◽

Top Predators ◽

Data Loggers ◽

Two Peaks

Abstract. Sub-arctic environmental changes are expected to affect the ecology of marine top predators. We examined the characteristics of foraging behavior of two sympatric congeneric diving seabirds, common (Uria aalge: hereafter COMU) and thick-billed (U. lomvia: hereafter TBMU) murres breeding on St. George Island located in the seasonal sea-ice region of the Bering Sea. We investigated their flight duration, diel patterns of dive depth, and underwater wing strokes, along with morphology and blood stable isotopes. Acceleration-temperature-depth data loggers were attached to chick-guarding birds, and behavioral data were obtained from 7 COMU and 12 TBMU. Both species showed similar trip duration (13.21 ± 4.79 h for COMU and 10.45 ± 7.09 h for TBMU) and similar diurnal patterns of diving (frequent dives to various depths in the daytime and less frequent dives to shallow depths in the nighttime). During the daytime, dive depths of COMU had two peaks in shallow (18.1 ± 6.0 m) and deep (74.2 ± 8.7 m) depths, while those of TBMU were 20.2 ± 7.4 m and 59.7 ± 7.9 m. COMU showed more frequent wing strokes during the bottom phase of dives (1.90 ± 0.11 s−1) than TBMU (1.66 ± 0.15 s−1). Fishes occurred with higher proportion in the bill-loads brought back to chicks in COMU (85 %) than in TBMU (56 %). δ15N value of blood was significantly higher in COMU (14.47 ± 0.27 ‰) than in TBMU (13.14 ± 0.36 ‰). Relatively small wing area (0.053 ± 0.007 m2) of COMU compared to TBMU (0.067 ± 0.007 m2) may make them more agile underwater and thus enable them to target more mobile prey including larger fishes that inhabit deeper depths. These differences in foraging behavior between COMU and TBMU might explain the differences in their responses to long-term marine environmental changes.

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The relationship between pink salmon biomass and the body condition of short-tailed shearwaters in the Bering Sea: can fish compete with seabirds?

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2010.2345 ◽

2011 ◽

Vol 278 (1718) ◽

pp. 2584-2590 ◽

Cited By ~ 16

Author(s):

Kanako Toge ◽

Rei Yamashita ◽

Kentaro Kazama ◽

Masaaki Fukuwaka ◽

Orio Yamamura ◽

...

Keyword(s):

Body Condition ◽

Bering Sea ◽

Pink Salmon ◽

The Body ◽

Oncorhynchus Gorbuscha ◽

Catch Per Unit Effort ◽

Study Region ◽

Top Predators ◽

The Relationship ◽

The Bering Sea

Seabirds and large fishes are important top predators in marine ecosystems, but few studies have explored the potential for competition between these groups. This study investigates the relationship between an observed biennial change of pink salmon ( Oncorhynchus gorbuscha ) biomass in the central Bering Sea (23 times greater in odd-numbered than in even-numbered years) and the body condition and diet of the short-tailed shearwater ( Puffinus tenuirostris ) that spends the post-breeding season there. Samples were collected with research gill nets over seven summers. Both species feed on krill, small fishes and squid. Although the mean pink salmon catch per unit effort (in mass) over the study region was not related significantly with shearwater's stomach content mass or prey composition, the pink salmon biomass showed a negative and significant relationship with the shearwater's body mass and liver mass (proxies of energy reserve). We interpret these results as evidence that fishes can negatively affect mean prey intake of seabirds if they feed on a shared prey in the pelagic ecosystem.

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Antarctic petrels ‘on the ice rocks’: wintering strategy of an Antarctic seabird

Royal Society Open Science ◽

10.1098/rsos.191429 ◽

2020 ◽

Vol 7 (4) ◽

pp. 191429 ◽

Cited By ~ 2

Author(s):

K. Delord ◽

A. Kato ◽

A. Tarroux ◽

F. Orgeret ◽

C. Cotté ◽

...

Keyword(s):

Sea Ice ◽

Environmental Changes ◽

Foraging Ecology ◽

Strong Association ◽

Euphausia Superba ◽

Sea Ice Concentration ◽

Seabird Species ◽

Ice Concentration ◽

Myctophid Fish ◽

Individual Use

There is a paucity of information on the foraging ecology, especially individual use of sea-ice features and icebergs, over the non-breeding season in many seabird species. Using geolocators and stable isotopes, we defined the movements, distribution and diet of adult Antarctic petrels Thalassoica antarctica from the largest known breeding colony, the inland Svarthamaren, Antarctica. More specifically, we examined how sea-ice concentration and free-drifting icebergs affect the distribution of Antarctic petrels. After breeding, birds moved north to the marginal ice zone (MIZ) in the Weddell sector of the Southern Ocean, following its northward extension during freeze-up in April, and they wintered there in April–August. There, the birds stayed predominantly out of the water (60–80% of the time) suggesting they use icebergs as platforms to stand on and/or to rest. Feather δ 15 N values encompassed one full trophic level, indicating that birds fed on various proportions of crustaceans and fish/squid, most likely Antarctic krill Euphausia superba and the myctophid fish Electrona antarctica and/or the squid Psychroteuthis glacialis . Birds showed strong affinity for the open waters of the northern boundary of the MIZ, an important iceberg transit area, which offers roosting opportunities and rich prey fields. The strong association of Antarctic petrels with sea-ice cycle and icebergs suggests the species can serve, year-round, as a sentinel of environmental changes for this remote region.

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Differential responses of seabirds to inter-annual environmental change in the continental shelf and oceanic habitats of southeastern Bering Sea

Biogeosciences Discussions ◽

10.5194/bgd-12-17693-2015 ◽

2015 ◽

Vol 12 (21) ◽

pp. 17693-17720 ◽

Cited By ~ 3

Author(s):

T. Yamamoto ◽

N. Kokubun ◽

D. M. Kikuchi ◽

N. Sato ◽

A. Takahashi ◽

...

Keyword(s):

Continental Shelf ◽

Bering Sea ◽

Physiological Stress ◽

Ocean Basin ◽

Ecosystem Dynamics ◽

Seabird Species ◽

Oceanic Basin ◽

Top Predators ◽

Differential Responses ◽

Year 2013

Abstract. Seasonal sea-ice cover has been decreasing in the southeastern Bering Sea shelf, which might affect ecosystem dynamics and availability of food resources to marine top predators breeding in the region. In this study, we investigated the foraging responses of two seabird species, surface-foraging red-legged kittiwakes Rissa brevirostris (hereafter, RLKI) and pursuit-diving foraging thick-billed murres Uria lomvia (TBMU) to the inter-annual change in environmental conditions. Between the study years, winter ice retreated earlier and summer water temperatures were warmer in 2014 compared to those in 2013. At-sea distributions of RLKI and TBMU breeding on St. George Island, the largest seabird colony in the region, were recorded using GPS loggers, and blood samples were taken to examine their physiological condition and isotopic foraging niche in a given year. RLKI foraging occurred mostly over the oceanic basin in both years. TBMU, however, foraged mostly over the shelf, but showed a relatively higher use of the shelf break and oceanic basin in the colder year, 2013. The foraging distances from the colony peaked at 250–300 km in 2013 and, bimodally, at 150–250 and 300–350 km in 2014 for RLKI, and tended to be farther in 2013 compared to those in 2014 for TBMU. Plasma levels of corticosterone did not differ between years in RLKI, but differed in TBMU, showing higher levels of physiological stress incurred by murres during the colder year, 2013. δ13N (a proxy of trophic level of prey) did not differ between the years in either RLKI or TBMU, while δ13C (a proxy of prey origin) were lower in 2014 than in 2013 in both species, suggesting possible differences in influx of oceanic prey items into foraging areas. These results suggest that the response of ecosystem dynamics to climate variability in the southeast Bering Sea may differ between the ocean basin and continental shelf regions, which, in turn, may generate differential responses in seabirds relying on those habitats for foraging.

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