The links between plumage variation and nest site occupancy in male House Sparrows

We examined patterns of nest site occupancy in male House Sparrows (Passer domesticus) to determine if the factors influencing nest site ownership are associated with a putative signal of resource-holding potential. No other study of House Sparrows has examined the correlates of nest site occupancy, despite their importance for understanding how the size of the bib (the patch of black feathers on throat and chest) might influence nest defense. We found that older males and males hatched on our study site were more likely than younger and immigrant males to occupy nest sites. Prior residency (the number of years a male had previously occupied a site) and not age had the greatest influence upon nest site retention between seasons. We found no influence of body size or the area of the bib on the probability of obtaining a nest site. Males hatched on the study site did not differ in bib size from males presumed to have immigrated from elsewhere. Bib size of individual males increased with age, but not years of prior residency. Males that consistently defended a nest site increased in bib size between years, whereas males that consistently failed to defend a nest site decreased in bib size. Bib size also tended to decrease in males that lost a nest site between seasons and increase in males that gained a nest site. Bib size thus may signal age and some types of experience in nest defense, although the details of its role in influencing contests over nest sites remain unclear.