Biology ETDs

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Naturally occurring populations of three species of colonial, altricial birds, the Piñon Jay (Gymnorhinus cyanocephalus), Great-tailed Grackle (Cassidix mexicanus) and Barn Swallow (Hirundo rustica) were tested for egg discrimination and the presence of intraspecific brood parasitism such discrimination would imply. Current theory predicts that, based on the intense pressure to increase personal fitness, brood parasitism, or cheating, should occur when a brood parasite's fitness is enhanced relative to a nonparasite's. Due to the high costs of parental care in altricial birds, selection against such cheaters (actual or potential) should also be intense. Egg rejection is the most common selection mechanism against interspecific brood parasites, and the absence or presence of this mechanism was tested for. Single eggs were switched between pairs of nests for each species and a fifth egg added to some Pinon Jay nests. Two entire Barn Swallow clutches were switched, and single Empidonax flycatcher eggs (species unknown) were added to two Barn Swallow nests. Based on this lack of evidence for a selective mechanism against cheaters it is hypothesized for these three species that either the pressure for such cheating is not so intense and, cheating, given what the behavior might cost, is rarer than to be expected, or that egg discrimination and rejection are not the mechanisms of selection against cheaters in these populations.



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Department Name

UNM Biology Department

First Committee Member (Chair)

J. David Ligon

Second Committee Member

Randy Thornhill

Third Committee Member

James Smith Findley

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Biology Commons