Zino's Petrel - Description

Description

This long-winged petrel is 32–34 cm (12.5–13.4 in) long with an 80–86 cm (31–34 in) wingspan, and an average weight of 290 g (10.3 in). It has a grey back, grey wings with a dark "W" marking across them, and a grey upper tail. The undersides of the wings are blackish apart from a triangle of white at the front edge near the body, and the belly is white with grey flanks. The head has a mottled whitish-brown forehead, a dark cap, and a dark spot below and behind the brown eye. The bill is black and the legs are flesh pink, the colour continuing onto the first third of the feet, the rest of the toes and webs being black-brown. It gives the general impression of a small Cory's or Great Shearwater, with a fast flight; in strong winds it shears high above the surface with angled wings. Nothing is known of the fresh juvenile plumage or the moult sequence, and ageing birds is currently not feasible.

This species is very similar in appearance to the Fea's Petrel, but is smaller. The size difference and lighter flight may not be apparent at sea, especially with lone birds, but a recent study helped to clarify other useful features. Zino's has a diagnostically small, delicate, often rather long and slender bill, which may be obvious in the most slender-billed examples, which are probably mostly females, but can be difficult to determine in larger-billed, probably adult male, birds. Another useful feature is a large whitish panel on the underwing. The wing panel is exclusive to Zino's but is only shown by 15% of the birds. Zino's has a more rounded wing tip, but P. feae deserti sometimes shows a rounded wing tip, so this feature is not diagnostic. Previously suggested criteria such as head, upperwing and flank patterns were found to be inconclusive. Off the eastern United States and the Azores, both Macronesian petrels are easily distinguished from the larger Bermuda Petrel by that species' upperparts, which are uniformly dark but for a pale grey rump.

This species at its breeding sites gives a long mournful call like the hooting of a Tawny Owl, and a much less frequent sound like the whimpering of a pup. It is silent at sea. The breeding calls are very similar to those of Fea's Petrel, and Bretagnolle's analysis of the calls of the Soft-plumaged Petrel complex led him to suggest in 1995 only a two-way species split, with the northern forms madeira, feae and deserti all as subspecies of Fea's Petrel.