Animalia Life

Oceanodroma leucorhoa
SUBFAMILY
Hydrobatinae
TAXONOMY
Oceanodroma leucorhoa Vieillot, 1818, maritime parts of Picardy. O. l. leucorhoa: all North Atlantic and North Pacific populations south to California. Populations in eastern Pacific vary in size and degree of white on rump; O. l. chapmani: breeds on San Benitos and Los Coronados islands, Mexico. O. l. socorrensis: breeds in summer on islets off Guadalupe Island, Mexico. O. l. cheimomnestes: breeds in winter on islets off Guadalupe Island, Mexico.
OTHER COMMON NAMES
French: Pйtrel culblanc; German: Wellenlaьfer; Spanish: Paiсo de Leach. PHYSICAL CHARACTERISTICS 7.0–8.5 in (180–220 mm); 1.3–1.9 oz (38–54 g). Mediumsized storm-petrel with white rump patch and distinctly forked tail, blackish brown above and below with paler diagonal upperwing bar from carpal joint back to trailing edge near body. Strongly downhooked bill and prominent nostrils. Legs and feet black. Sexes alike. Flight less fluttering than that of Wilson’s storm-petrel and wings tend to be held more horizontally than those of Wilson’s storm-petrel (which raises its wings into a V). Feet not visible beyond tail and much less prone to pattering.
DISTRIBUTION
Breeds on islands in the North Atlantic and North Pacific that lack mammalian predators. Found at sea throughout these seas, migrates south into the tropics after breeding. Pairs have even been found in burrows on the Chatham Islands, New Zealand. One bird was found on St. Croix Island, South Africa, which suggests the possibility of extending the breeding range southwards. The eastern North American populations shift south to Brazilian waters but many cross to European seas like the Bay of Biscay. British breeders appear to winter mainly off tropical Africa. Japanese and Alaskan birds also winter in tropical seas.
HABITAT
Ranges widely in the open sea. California birds feed farther out in warmer, less productive seas than do ashy and fork-tailed storm-petrels with which they often share nesting islands.
BEHAVIOR
On land, overflying birds that emit calls are mainly prebreeders; nesting birds call mostly from their burrows. Little display occurs between breeding birds except persistent calling using two main types of rhythmic purrings and chatterings. Chatter calls are given from the air and the burrow, and research in Japan suggests that variation in the pitch of calls among birds of the same sex may be used for individual recognition.
FEEDING ECOLOGY AND DIET
Nekton and planktonic organisms are taken from the surface while the bird hovers facing the wind, sometimes alighting momentarily. Otherwise the flight is a mixture of gliding and rather wild dashes, with many changes of direction. Seldom follows ships but is prone to be wrecked on beaches during gales. Diet includes a great range of fish, crustaceans, and squid as available. The birds tend to seek areas where upcurrents bring organisms to the surface. Their stomachs often contain deepsea animals that only approach the surface at night, evidently taken after dark. They appear to find some prey using their good sense of smell.
REPRODUCTIVE BIOLOGY
Most breed at around five years old. Having gained a nest site, a pair remains intact as long as they reproduce satisfactorily. Most dig burrows, but some occupy crevices among rocks or stone walls. The single egg is occasionally replaced if it is lost soon after laying. Both sexes incubate in 2–3 day shifts for about 43 days. Chick is fed almost nightly in the first few days after the brief brooding period, then less often as it grows. Unfed chicks become torpid but can recover. Growth follows the normal curve: weight climbs steadily at a constant rate, levels out at above parental weight, then falls in the last 10 or so days before fledging. Fledging occurs when the chick is between 56 and 79 days. The number of chicks fledged per egg laid differs between seasons and places and ranges from 48 to 73%. Losses have often been due to introduced mammals like mink, cats, and others, but natural predators also include owls, eagles, corvids, and gulls.
CONSERVATION STATUS
Not threatened, but existing colonies need protection against the introduction of placental mammals and trampling of burrows.
SIGNIFICANCE TO HUMANS
None known.

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