Introduction

The Black Storm-Petrel inhabits tropical, subtropical, and warm-temperate waters of the extreme eastern North Pacific Ocean, where it nests in desert habitat on islands. Its breeding range overlaps broadly with several other all-dark Oceanodroma storm-petrels, often cohabiting the same islands and even (sometimes sequentially) the same nesting crevices. Nesting habitat is divided on the basis of a nesting cavity-size to body-size relationship. As is true of most all-dark forms, Black Storm-Petrels do not excavate their own nesting cavities, but many other storm-petrel species do. Like almost all storm-petrels, this one is active at colonies only at night, a defense against avian predators. Breeding populations are limited by availability of nesting habitat and have been affected immensely in modern times by the introduction of feral and predatory mammals to islands.

This species exhibits an unusual bifurcation of wintering grounds, characteristic of other seabirds nesting in the Gulf of California. It largely vacates the central nesting region of the Gulf of California and southern Pacific Baja California coast, with some portion moving north to waters off southern and central California and another, larger portion, moving south to waters off Central America and northern South America. Bifurcation may be an adaptive strategy to avoid entrapment by hurricanes in the Gulf and along the adjacent Mexican coast.

The Black Storm-Petrel has been little studied on its nesting grounds, owing to its small breeding populations on California islands and the difficult habitat occupied on Baja California islands (mainly, dense growth of cactus). What little is known mostly confirms the species’ basic storm-petrel life-history strategy: nocturnal visitation, burrow-nesting, 1 egg clutch, slow chick growth, etc. (cf. Everett 1991, Ainley 1995, Huntington et al. 1996). What is remarkable is the concentration of so many storm-petrel species among the Baja California and southern (Alta) California islands, with diversification seemingly related to body size and use of marine habitat. Black Storm-Petrel is the largest, is quasimigratory, and is the most inshore of the group. Whether size affects prey choice is a question that remains to be answered.