AVIS-IBIS

Birds of Indian Subcontinent

Natural Selection and Sexual Dimorphism: Sex-Biased Sparrowhawk Predation Favours Crypsis in Female Chaffinches

Publication Type:Journal Article
Year of Publication:1997
Authors:Götmark, F, Post, P, Olsson, J, Himmelmann, D
Journal:Oikos
Volume:80
Issue:3
Date Published:1997
ISBN Number:00301299
Keywords:Accipiter, Accipiter nisus, Accipitridae, Fringilla, Fringilla coelebs, Fringillidae
Abstract:A general assumption is that bright colours, song and other traits of male birds lead to high predation risk; lower risk is often assumed for the more cryptic females. However, the reversed scenario is also a theoretical possibility, as breeding females spend much time foraging, which may increase predation. We examined predation on breeding chaffinches Fringilla coelebs by sparrowhawks Accipiter nisus, the major predators of this species. Assuming male biased sex ratio, or sex ratio of unity, significantly more females than males were taken by hawks (especially in a year with harsh weather). The idea that bright male plumage is a signal of 'unprofitable prey' was tested by exposing pairs of stuffed chaffinches near hawk nests. We found no support for this idea, as the hawks did not avoid the males. Female chaffinches spent more time foraging and were more active and closer to the ground than males; they were therefore probably easier to detect and catch for sparrowhawks. Thus, predation probably selects for crypsis in female chaffinches. Higher predation risk that favours crypsis in females is one of the reasons for sexual dimorphism in plumage in this and presumably also other passerine birds.
URL:http://www.jstor.org/stable/3546627
Short Title:Oikos
Taxonomic name: 
Accipiter (Birds), Accipiter nisus (Birds), Accipitridae (Birds), Fringilla (Birds), Fringilla coelebs (Birds), Fringilla coelebs (Birds), Fringillidae (Birds)
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith