First Record of Cannibalism in Socotra Cormorants (<i>Phalacrocorax nigrogularis</i>): Large, Immature Birds Opportunistically Feed on Younger Conspecifics

Gubiani, Robert; Benjamin, Sonya; Muzaffar, Sabir Bin

doi:10.1675/063.035.0215

Cited by 10 publications

(5 citation statements)

References 9 publications

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“…Our observation of cannibalism was recorded during the second breeding season, when there was a significant reduction in the consumption of penguins and flying birds by South Polar skua, which may have made this behavior more likely. Cannibalism has also been linked to food shortages in other seabird species, such as Socotra Cormorant (Phalacrocorax nigrogularis) (Gubiani et al 2012) and Longtailed jaeger (Stercorarius longicaudus) (Vooren & Chiaradia1989). Carneiro et al (2010) suggested that, at Admiralty Bay, if breeding pairs of South Polar skua attempt to settle a territory defended by Brown skuas, in the vicinity of a penguin colony, their eggs and chicks may be subject to predation by Brown skua, although further studies are required to confirm this relationship.…”

Section: Discussionmentioning

confidence: 99%

Pellets and Prey Remains as Indicators of the Diet of Two Sympatric Skuas (Aves: Stercorariidae) on King George Island, Antarctica

et al. 2021

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South Polar skua (Stercorarius maccormicki) and Brown skua (Stercorarius antarcticus lonnbergi) have opportunistic feeding habits and are the dominant predators in terrestrial Polar regions. These skuas exploit a wide range of food items, including marine organisms, other birds, and even garbage. In the present study, we compare the diets of these two skua species during the breeding season, using pellets and prey remains collected within their territories. The samples were collected at six sites in Admiralty Bay, on King George Island, Antarctica. We identified eight different items, which we classified as “penguin”, “flying bird”, “skua”, “fish”, “gastropod”, “krill”, “egg” and “marine debris”. In the first breeding season (2008/2009), penguins and flying birds were the food resources more abundant for both skua species, and their diet composition was similar. In the second breeding season (2010/2011) South Polar skua exploited more fish and flying birds than Brown skua; the latter exploited more eggs and penguins. Our findings corroborate those of previous studies, demonstrating that in sympatry South Polar skua exploit more fish than Brown skua. The diet of South Polar skua also varied between breeding seasons, reflecting the opportunistic foraging behavior of these skuas. As in other studies, we recorded that skua is a food resource for both skua species, but it was more common in the diet of South Polar skua. Marine debris was recorded only in the samples of Brown skua. Birds are important food items for both skuas, although significant differences were found in the diets of these sympatric species, with shifts in the composition of the diet probably reflecting fluctuations in the abundance of prey populations, which are known to be common at Admiralty Bay, although more data will be needed to confirm this link.

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Section: Discussionmentioning

confidence: 99%

Pellets and Prey Remains as Indicators of the Diet of Two Sympatric Skuas (Aves: Stercorariidae) on King George Island, Antarctica

et al. 2021

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“…Each noose was set around the edge of the nest, which is a cup built in sand. Birds were captured during the late incubation/hatchling stage because eggs and hatchlings (naked altricial chicks younger than 2 weeks old, following Gubiani, Benjamin, & Muzaffar, ) are not in danger of being caught in the noose, while older chicks may accidently become snared because of their larger size. Culmen and tarsus of adults were measured using a Vernier caliper.…”

Section: Methodsmentioning

confidence: 99%

Group foraging in Socotra cormorants: A biologging approach to the study of a complex behavior

Cook

Gubiani

Ryan

et al. 2017

Ecology and Evolution

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Group foraging contradicts classic ecological theory because intraspecific competition normally increases with aggregation. Hence, there should be evolutionary benefits to group foraging. The study of group foraging in the field remains challenging however, because of the large number of individuals involved and the remoteness of the interactions to the observer. Biologging represents a cost‐effective solution to these methodological issues. By deploying GPS and temperature–depth loggers on individuals over a period of several consecutive days, we investigated intraspecific foraging interactions in the Socotra cormorant Phalacrocorax nigrogularis, a threatened colonial seabird endemic to the Arabian Peninsula. In particular, we examined how closely birds from the same colony associated with each other spatially when they were at sea at the same time and the distance between foraging dives at different periods of the day. Results show that the position of different birds overlapped substantially, all birds targeting the same general foraging grounds throughout the day, likely following the same school of fish. There were as many as 44,500 birds within the foraging flock at sea at any time (50% of the colony), and flocking density was high, with distance between birds ranging from 8 to 1,380 m. Birds adopted a diving strategy maximizing time spent underwater relative to surface time, resulting in up to 72% of birds underwater in potential contact with prey at all times while foraging. Our data suggest that the benefits of group foraging outweigh the costs of intense aggregation in this seabird. Prey detection and information transmission are facilitated in large groups. Once discovered, shoaling prey are concentrated under the effect of the multitude. Fish school cohesiveness is then disorganized by continuous attacks of diving birds to facilitate prey capture. Decreasing population size could pose a risk to the persistence of threatened seabirds where group size is important for foraging success.

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“…We approached nesting cormorants during 14.00–16.00, which elicited regurgitation (normally they would attempt to feed the chicks directly). In the 2011–2012 breeding season sampling was carried out early (17 October 2011), when most chicks (> 75%) had hatched but were still small and associated with nests, and late (19 November 2011), when chicks were > 2 weeks old and many were still associated with nest sites but most were forming creches (Gubiani et al, 2012). Thus, there was a better representation of the diet of chicks of various sizes during 2011–2012.…”

Section: Methodsmentioning

confidence: 99%

Food consumption patterns of the Vulnerable Socotra cormorant Phalacrocorax nigrogularis indicate minimal overlap with fisheries in the eastern Arabian Gulf

Muzaffar

Gubiani

Benjamin

et al. 2015

Oryx

Self Cite

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Historically cormorants have come into direct conflict with fisheries because of their feeding habits. The Socotra cormorant Phalacrocorax nigrogularis is a regionally endemic seabird restricted to the Arabian Gulf and coastal Oman, and is categorized as Vulnerable on the IUCN Red List. The species is perceived as being detrimental to local fisheries and is therefore persecuted. We studied the diet and estimated the number of Socotra cormorants breeding on Siniya Island, Umm Al Quwain, United Arab Emirates, to determine their impact on local fisheries. Regurgitated fish loads were collected during the breeding seasons of - and -, and the biomass of fish consumed by the Socotra cormorant population was estimated. The diet comprised seven species of fish, with sailfin flying fish Parexocoetus mento and blue-stripe sardine Herklotsichthys quadrimaculatus dominating in - and anchovies (Encrasicholina spp.) dominating in -. Biomass of fish loads was higher in - compared to -, although mean biomass of fish loads did not differ. Dominant fish species in the cormorant's diet were either used as baitfish or were non-target species in the fisheries. The low overlap between the diet of the Socotra cormorant and the fish landed by the fisheries suggests that the cormorant's impact on fisheries is minimal. Conservation strategies to protect the birds and their feeding areas could safeguard populations of this species from further declines.

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First Record of Cannibalism in Socotra Cormorants (Phalacrocorax nigrogularis): Large, Immature Birds Opportunistically Feed on Younger Conspecifics

Cited by 10 publications

References 9 publications

Pellets and Prey Remains as Indicators of the Diet of Two Sympatric Skuas (Aves: Stercorariidae) on King George Island, Antarctica

Pellets and Prey Remains as Indicators of the Diet of Two Sympatric Skuas (Aves: Stercorariidae) on King George Island, Antarctica

Group foraging in Socotra cormorants: A biologging approach to the study of a complex behavior

Food consumption patterns of the Vulnerable Socotra cormorant Phalacrocorax nigrogularis indicate minimal overlap with fisheries in the eastern Arabian Gulf

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