Identification
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A long-winged, black-and-white bird that is most often found far out at sea, coming to land only to breed on remote cliffs from November into May. Adults visit the nest sites only at night, when it is possible to hear this species vocalizing. The rather similar Bermuda Petrel lacks this species’ white collar and white rump. Black-capped Petrels also have a darker headed or “cowled” appearance than Bermuda Petrels. Calls at nesting areas include a drawn out “awwwww” that often grows louder towards the end and is usually given in series, sometimes with a squeaky hiccuplike terminal note that has an oddly donkey-like quality. Also gives a puppy-like yelp.
Relative Size
Larger than Sargasso Shearwater and smaller than Great Shearwater.
Measurements
- Both Sexes
- Length: 13.8-18.1 in (35-46 cm)
- Weight: 11.6-20.9 oz (329-591 g)
Regional Differences
Black-capped Petrels occur in two distinct forms: a “White-faced” form and a “Dark-faced” form. It's not clear whether there is a geographic basis for this variation. The “White-faced” form is slightly larger and molts earlier. It has a smaller black cap that is interrupted by a thin white line above the eye, making the black eye stand out against a white face. The White-faced form typically has a distinct white collar that contrasts with the black cap. The slightly smaller “Dark-faced” form, which molts later, has a larger black cap that surrounds the dark eye. This form has a brownish collar, resulting in a lack of a clean white break between the black cap and dark upperparts. The “Dark-faced” form also has a wide dark spur on the side of the chest, whereas the “White-faced” form has at most a narrow chest spur. Intermediate birds also exist.
