Breeding biology of storm-petrels at Wooded Islands, Alaska

Abstract

Fork-tailed and Leach’s Storm-Petrels were studied at Wooded Islands, Alaska, 59°52‘ N, 147°25’W, to document and compare their breeding biology. Measurements of both species from California to the Aleutian Islands showed clinal variation; current subspecies divisions are not justified. Fork-tailed Storm-Petrels nested in a wider variety of habitats, arrived earlier at night, nested earlier, and fledged young in a shorter period than Leach’s Storm-Petrels, apparently because of their different oceanic distributions. River otter predation was the major cause of nest failures. Nesting success was higher within an exclosure than in areas exposed to predation. Predation was greater at low than high nest densities, and greater in soil than in rock habitat. Continued otter predation may decimate soil-nesting populations. Fork-tailed Storm-Petrel chick growth patterns did not vary between habitats, or nest densities. Mid- and late hatched fork-tail chicks grew faster, attained heavier weights, and had shorter nestling periods than early hatched chicks.