Sympatry of Laysan and Black-Footed Albatrosses

Abstract

IF we assume that albatrosses arose in the Southern Hemisphere where the greatest number of forms occur today, the three species in the North Pacific are derivatives of southern stock. They are isolated from significant ingress of genotypes from the southern species by the broad band of warm, unsuitable waters near the equator. Few southern species are known even as vagrants north of 200 S. The extreme southern record for a North Pacific species is 8? N (Thompson, 1951), and most individuals stay north of 200 N. The three species of North Pacific albatrosses are: the Laysan, Diomedea immutabilis; the Black-footed, D. nigripes; and the Short-tailed, D. albatrus. The Short-tailed Albatross is outside the scope of this paper because its close affinities appear to lie with the great albatrosses, D. exulans and D. epomophora, rather than with the Laysan and Blackfooted species. It probably represents a northward immigration separate from that of the other two species. The purpose of this discussion is to present some views of the origin and subsequent sympatry of the Laysan and Black-footed albatrosses over virtually all their breeding range. These two species have much in common, despite the major difference in coloration. The more significant similarities lie in the blood proteins (Brown and Fisher, 1966) and the courtship display, which is more complex than in Southern Hemisphere forms; both sexes regularly participate and exhibit the dorsum rather than the ventrum of the wing to the partner. The species are close in body size, breeding season, incubation period, pattern of sexual participation in incubation, and vocalization. And in many of these features they also show important variations from southern species.