Parkinson's 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"N) to northern Peru (ca. 5"S), and along a broad seaward extension that continued west of the Galapagos Islands to 11O"W. Parkinson' s Petrels regularly associated with dolphins: of the 6 18 petrels observed, 469 (76%) were associated with 10 species of dolphins, on 55 occasions, with 1 to 300 petrels
... h 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 con- sisted 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.