Diet and Foraging

Little information is available on the diet of Black-capped Petrel. Current information is based on the examination of the stomachs of 60 individuals collected at sea off the coast of the US (68 Haney, J. C. (1987). Aspects of the pelagic ecology and behaviour of the Black-capped Petrel (Pterodroma hasitata). Wilson Bulletin 99(1):153–168. Close , 71 Moser, M. L., and D. S. Lee (1992). A fourteen-year survey of plastic ingestion by western North Atlantic seabirds. Colonial Waterbirds 15:83–94. Close ), and on a molecular analysis of fecal DNA from adult petrels captured at breeding sites and at sea (YGS, unpublished data).

Main Foods Taken

Historically suspected to feed mostly on squid and fish (5 Simons, T. R., D. S. Lee, and J. C. Haney (2013). Diablotin Pterodroma hasitata: a biography of the endangered Black-capped Petrel. Marine Ornithology 41:S3–S43. Close ). Recent molecular analysis of fecal DNA suggests a higher diversity of prey, including meso- and bentho-pelagic fish taxa (YGS, unpublished data).

Microhabitat for Foraging

Petrels forage in association with upwellings and fronts induced by eddies (see Habitat). This species typically does not follow ships, although individuals may investigate "chum" slicks for potential food. Black-capped Petrel may feed in multispecific rafts, or individually, picking food items such as squid from the ocean surface.

Food Capture and Consumption

Simons et al. (5 Simons, T. R., D. S. Lee, and J. C. Haney (2013). Diablotin Pterodroma hasitata: a biography of the endangered Black-capped Petrel. Marine Ornithology 41:S3–S43. Close ) wrote a detailed discussion of the feeding behavior. We share the main observations here, but encourage readers interested in the details of timing of feeding activity, association with other seabirds, response to chum and offal, and expected visual clues to refer to that publication.

Most Black-capped Petrel feeding activity occurs at night or early in the morning, although birds are often seen feeding during mid-day (5 Simons, T. R., D. S. Lee, and J. C. Haney (2013). Diablotin Pterodroma hasitata: a biography of the endangered Black-capped Petrel. Marine Ornithology 41:S3–S43. Close ). The prominence of pelagic Cephalopoda in their diet suggests an adaptation for crepuscular or nocturnal feeding, given that this prey type undergoes nocturnal diel migrations.

The majority of feeding bouts reported by Haney (68 Haney, J. C. (1987). Aspects of the pelagic ecology and behaviour of the Black-capped Petrel (Pterodroma hasitata). Wilson Bulletin 99(1):153–168. Close ) occurred within flocks (96%), 88% of which included other species (n = 25); these flocks may contain numerous Black-capped Petrels, with up to 65 observed at once (68 Haney, J. C. (1987). Aspects of the pelagic ecology and behaviour of the Black-capped Petrel (Pterodroma hasitata). Wilson Bulletin 99(1):153–168. Close ). Petrels were observed feeding at “baitfish” or invertebrate swarms with 12 other species and averaged 4.3 species per feeding flock (range 2–8 species/flock). The most frequent associates were Cory's Shearwater (Calonectris diomedea), Great Shearwater (Ardenna gravis), Audubon's Shearwater (Puffinus lherminieri), and Pomarine Jaeger (Stercorarius pomarinus) in summer, and Herring Gull (Larus argentatus) and Black-legged Kittiwake (Rissa tridactyla) during the winter. Petrels fed with 10 seabird species (mean 3.8 species/flock, range 3–6) at chum slicks, including Great Shearwater, Wilson's Storm-Petrel (Oceanites oceanicus), and Pomarine Jaeger in summer and Herring Gull and Laughing Gull (Leucophaeus atricilla) in winter. Less common feeding associates observed by Lee (in 72 Haney, J. C., D. S. Lee, and R. D. Morris. 1999. Bridled Tern (Sterna anaethetus). In The Birds of North America, No. 468 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA. Close ) included South Polar Skua (Stercorarius maccormicki), Common Tern (Sterna hirundo), Bridled Tern (Onychoprion anaethetus), and Sooty Tern (Onychoprion fuscatus). With limited exceptions, Black-capped Petrel is not usually seen in association with marine mammals. Lee (in 5 Simons, T. R., D. S. Lee, and J. C. Haney (2013). Diablotin Pterodroma hasitata: a biography of the endangered Black-capped Petrel. Marine Ornithology 41:S3–S43. Close ) observed a single petrel foraging around a fin whale (Balaenoptera physalus), which was Lee’s only record of Black-capped Petrel in shallow (< 30 m) shelf waters. Offshore Hatteras, North Carolina, it has been seen occasionally in association with sperm whales (Physeter macrocephalus), pilot whales (presumably short-finned, Globicephala macrorhynchus), and Risso’s dolphins (Grampus griseus) (KES, unpublished data).

As do other species of gadfly petrels, Black-capped Petrel has been observed seizing prey at or just beneath the surface (68 Haney, J. C. (1987). Aspects of the pelagic ecology and behaviour of the Black-capped Petrel (Pterodroma hasitata). Wilson Bulletin 99(1):153–168. Close ). It uses at least four foraging postures when feeding: sitting on the ocean surface; aerial dipping and pattering; aerial maneuvering; and, less commonly, sitting on the ocean surface with head and neck submerged underwater (5 Simons, T. R., D. S. Lee, and J. C. Haney (2013). Diablotin Pterodroma hasitata: a biography of the endangered Black-capped Petrel. Marine Ornithology 41:S3–S43. Close ). Though it is commonly mentioned that petrels have “never [been] seen to submerge beneath the ocean surface” (5 Simons, T. R., D. S. Lee, and J. C. Haney (2013). Diablotin Pterodroma hasitata: a biography of the endangered Black-capped Petrel. Marine Ornithology 41:S3–S43. Close ), on a few occasions they were observed and photographed diving underwater for some extent of time in search of natural food and chum (KES, unpublished data). Petrels have been observed arriving from upwind to investigate feeding sites, and therefore do not appear to rely exclusively on olfaction to locate food sources; instead, or in addition, they may use visual clues, with their high arching flight pattern facilitating visual detection of surface slicks (5 Simons, T. R., D. S. Lee, and J. C. Haney (2013). Diablotin Pterodroma hasitata: a biography of the endangered Black-capped Petrel. Marine Ornithology 41:S3–S43. Close ) and feeding groups.

Recent observations suggest that Black-capped Petrel may also kleptoparasitize other seabirds. On two occasions, at chum slicks for pelagic seabirds off Cape Hatteras, Black-capped Petrels have been observed chasing an Audubon's Shearwater (Puffinus lherminieri) and Fea's Petrel (Pterodroma feae), both with food (KES, unpublished data). Off the coast of Cape Verde, Stronach (73 Stronach, P. (2020). Black-capped Petrel kleptoparasitising Red-billed Tropicbirds off Raso, Cape Verde Islands, in February 2020. Dutch Birding 42:181–184. Close ) observed a Black-capped Petrel kleptoparasitizing several Red-billed Tropicbird (Phaethon aethereus) for 17 min, forcing two of them to regurgitate. It is unclear if this behavior is opportunistic or more regular.

Major Food Items

Moser and Lee (71 Moser, M. L., and D. S. Lee (1992). A fourteen-year survey of plastic ingestion by western North Atlantic seabirds. Colonial Waterbirds 15:83–94. Close ) examined the stomachs and crops of 57 Black-capped Petrel collected off North Carolina, which revealed the following (by frequency of occurrence): squid (93.0% of individuals), fish (49.1% of individuals), crustaceans (3.6% of individuals), pieces of Sargassum (14.0% of individuals), plastic (1.8% of individuals), unidentified items (17.5% of individuals), and empty (4% of individuals). Squid were the most frequently encountered food item, but undigestible beak fragments accumulate in crops and may create the false impression of a preference for squid (5 Simons, T. R., D. S. Lee, and J. C. Haney (2013). Diablotin Pterodroma hasitata: a biography of the endangered Black-capped Petrel. Marine Ornithology 41:S3–S43. Close ). A preliminary molecular analysis of prey DNA found in petrel feces suggests more fish are eaten than expected, particularly meso- and bentho-pelagic taxa (including fish that perform diel migrations; YGS, unpublished data).