PARKINSON PETREL DISTRIBUTION AND FORAGING ECOLOGY IN THE EASTERN PACIFIC - ASPECTS OF AN EXCLUSIVE FEEDING RELATIONSHIP WITH DOLPHINS

During 28 research vessel cruises in the eastern tropical Pacific Ocean from 1976 through 1990, Parkinson's Petrels (Procellaria parkinsoni) were observed near shore from southern Mexico (ca. 15-degrees-N) to northern Peru (ca. 5-degrees-S), and along a broad seaward extension that continued west of the Galapagos Islands to 110-degrees-W. Parkinson's Petrels regularly associated with dolphins: of the 6 1 8 petrels observed, 469 (76%) were associated with 10 species of dolphins, on 55 occasions, with 1 to 300 petrels present. They occurred mostly with two rare dolphin species: the melon-headed whale (Peponocephala electra) and the false killer whale (Pseudorca crassidens). This appeared to be a largely obligatory foraging relationship for Parkinson's Petrels. Associations with other dolphin species occurred primarily when those species also associated with melon-headed and false killer whales. Parkinson's Petrels avoided a common and widespread, multi-species feeding assemblage which consisted of a diverse, fast-moving group of seabirds, spotted and spinner dolphins (Stenella attenuata and S. longirostris), and tuna, all of which feed on live prey forced to the surface. The lumbering Parkinson's Petrels appeared ill-equipped to take such prey. In contrast, melon-headed and false killer whales apparently fed by dismembering large prey below the surface and so, provided feeding opportunities for a scavenging bird with diving capabilities. Among eastern tropical Pacific (ETP) seabirds, Parkinson's Petrels alone are adapted for recovering food scraps well below the surface. Parkinson's Petrels appear to be more dependent on marine mammals for foraging than any other species of seabird studied and feed diurnally more than was previously thought.