A Kleptoparasitic Chase by Brown Pelicans on a Western Gull

Abstract

interspecific kleptoparasitism, or the stealing of food from other species, is fairly widespread among birds, most frequently reported for seabirds, especially among the Charadriiformes (Brockman and Barnard 1979, Furness 1987, iyengar 2008). Though most kleptoparasitic species engage in this behavior facultatively, some (especially within the Charadriiformes) may be obligate kleptoparasites during a particular season and potentially throughout the year (iyengar 2008). Within the family Pelecanidae it has been infrequently reported in the literature. The ecology and behavior of seabirds meet many of the ecological factors proposed for the evolution of kleptoparasitism, including open habitat, feeding in mixed-species groups, scavenging, and the host’s habits being predictable (Brockman and Barnard 1979, Paulson 1985, iyengar 2008). Though kleptoparasitism often involves a larger species stealing food from a smaller species, the Brown Pelican (Pelecanus occidentalis) is perhaps better known as the victim of kleptoparasitism by smaller gulls than vice versa, with several species of gulls and terns reported to steal from it (Shields 2014). The Brown Pelican was the first species of pelican reported to kleptoparasitize (Sefton 1950, Brockmann and Barnard 1979), and this behavior has since been reported in the americas by the closely related Peruvian Pelican (P. thagus) (Duffy 1980) and the american White Pelican (P. erythrorhynchos) (O’malley and evans 1983, anderson 1991). reports of kleptoparasitic attacks by the Brown Pelican have appeared to be isolated incidents. in the Peruvian Pelican, however, Duffy (1983) reported that 18% of attempts to obtain prey involved piracy. most reported kleptoparasitic attacks by the Brown Pelican and closely related Peruvian Pelican have been in mixed feeding flocks where the pelican is sitting on the water and grabs with its bill or otherwise attacks a nearby species, getting it to drop its food (Sefton 1950, Duffy 1980, lanciani 2000). This is especially common in situations where the birds are feeding on offal being thrown by people, though it occurs regularly in “wild” situations as well (D. anderson pers. comm.). The Brown Pelican’s target species have included the Double-crested Cormorant (Phalacrocorax auritus) and unidentified gulls (Larus spp.), as well as other Brown Pelicans (D. anderson pers. comm.). Brown Pelicans have also been observed landing on Great Blue Herons (Ardea herodias) in order to get them to drop food (Bildstein 1980). O’malley and evans (1983) observed aerial chases by american White Pelicans in pursuit of food, but i am aware of no such observations involving the Brown Pelican. at ~16:30 on 19 October 2013, during an organized whale watch out of long Beach, California, in the vicinity of Platform ellen (Orange County), i noted a subadult (second-cycle) Western Gull (L. occidentalis) chasing an adult Western Gull, followed by two adult Brown Pelicans. The four birds were first seen flying parallel to the boat, about a kilometer away and only a few meters above the water. The second-cycle Western Gull was close behind the adult Western Gull with the two pelicans following about three meters behind the gulls. The adult gull banked up at roughly a 45° angle to a height of about 5 meters above the water before gliding back down in an attempt to escape. The second-cycle gull followed closely, and the pelicans also followed, banking up behind the gulls. The lead gull reversed course and quickly made a sharp ascent; through labored flight the pelicans were able to follow. While the second-cycle gull was able to stay on the tail of the lead gull, the pelicans fell back to about 10 meters behind both gulls. However, when the lead gull reversed course again, flying low over the water, both pelicans were able to shorten the gap and eventually overtake the second-cycle gull, placing nOTeS