| Titre : | Evidence of selection for egg crypsis in conspicuous nests |
| Auteurs : | David Westmoreland, Auteur |
| Type de document : | Article |
| Dans : | Journal of Field Ornithology (79(3) SEP 2008) |
| Article en page(s) : | 263-268 |
| Langues: | Anglais |
| Résumé : | The value of egg coloration as crypsis, once accepted as a general principle, has recently been questioned because most experiments have failed to show that egg coloration deters predation. The nest-crypsis hypothesis postulates that, among species that build conspicuous nests, selection for egg crypsis is relaxed or absent because visually searching predators detect nests prior to eggs. I tested the nest-crypsis hypothesis using the large, relatively conspicuous nests of American Robins (Turdus migratorius), and eggs that differed markedly in color that were collected from the nests of Red-winged Blackbirds (Agelaius phoeniceus), Brewer's Blackbirds (Euphagus cyanocephalus), and Yellow-headed Blackbirds (Xanthocephalus xanthocephalus). Each nest (N = 22) received a clutch of each species during three sequential predation trials that were 16 d in duration. The order of clutch presentation was randomized for each nest. Survival trends for Brewer's and Yellow-headed Blackbirds were similar, and higher than those for clutches of Red-winged Blackbirds. By the end of trials, overall survival of the three clutch types was roughly equivalent. However, clutches of Red-winged Blackbird eggs, the most conspicuous egg type to the human eye, were discovered sooner by predators. Because the experimental design controlled for effects of nest crypsis, nest location, and nest size, this difference in egg survival can be attributed to differences in egg pigmentation. Thus, my results support a role for egg coloration as camouflage in conspicuous nests. |
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