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Kleptoparasitism by Kermadec Petrels, Jaegers, and Skuas in the Eastern Tropical Pacific: Evidence of Mimicry by Two Species of Pterodroma

Larry Spear and David G. Ainley
The Auk
Vol. 110, No. 2 (Apr., 1993), pp. 222-233
Stable URL: http://www.jstor.org/stable/4088550
Page Count: 12
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Kleptoparasitism by Kermadec Petrels, Jaegers, and Skuas in the Eastern Tropical Pacific: Evidence of Mimicry by Two Species of Pterodroma
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Abstract

We studied the ecology and behavior of pelagic seabirds in the Eastern Tropical Pacific (1984-1992). We hypothesize that the absence of kleptoparasitism (hereafter "parasitism") by jaegers and skuas (subfamily Stercorariinae, hereafter "skuas") on Kermadec Petrels (Pterodroma neglecta) and Herald Petrels (P. arminjoniana) observed in this study, compared to regular attack on procellariids of similar size, resulted from Batesian mimicry by the former of skuas. As mimics of skuas, Kermadec and Herald petrels avoided being kleptoparasitized because skuas do not parasitize conspecifics. We also document regular parasitism by Kermadec Petrels on other large procellariids, and further hypothesize that this petrel is successful as a parasite because it is a foraging mimic of the subadults of the larger skuas (Pomarine Jaegers [Stercorarius pomarinus] and South Polar Skuas [Catharacta maccormicki]) through its similarity of color pattern, flight profile, and behavior when initiating an attack, and because the large skuas (its models) are very effective as parasites. This petrel's incidence of attack and frequent use of alternate feeding methods suggests that it is a less specialized parasite than are the skuas. Kermadec Petrels prefer the same hosts and use a similar method of attack as do the large skuas, which achieve a very high rate of success in the Eastern Tropical Pacific because of their ability to threaten hosts through size-mediated aggressiveness. The Kermadec Petrel is smaller or similar in size to its preferred hosts and is not as aggressive as large skuas, but its rate of success as a parasite is higher than expected.

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