Age, Plumage Brightness, Territory Quality, and Reproductive Success in the Black-Headed Grosbeak

Publication Type:Journal Article
Year of Publication:1988
Authors:Hill, GE
Journal:The Condor
Date Published:1988
ISBN Number:00105422
Keywords:Aphelocoma, Aphelocoma californica, Aphelocoma coerulescens, Cardinalidae, Corvidae, Cyanocitta, Cyanocitta stelleri, Eophona, Eophona migratoria, Fringillidae, Garrulus, Garrulus glandarius, Mexico, Pheucticus, Pheucticus melanocephalus
Abstract:I studied a color-banded population of Black-headed Grosbeaks (Pheucticus melanocephalus) in the Sandia Mountains of central New Mexico to investigate the relationship between the age and plumage brightness of territorial males and the quality of their breeding habitat. In three seasons of fieldwork, I found that the breeding territories defended by males varied in vegetation structure and hence in the abundance of Scrub Jays (Aphelocoma coerulescens) and Steller's Jays (Cyanocitta stelleri), the primary nest predators of grosbeaks. Age appeared to be the primary correlate of male territory quality. Males 3 years and older defended areas with heterogeneous vegetation and low density of jays and, consequently, had high reproductive success; yearling and 2-year-old males occupied more densely vegetated areas with higher jay activity and had lower reproductive success. Independent of age, there was also a tendency for brightly plumaged males to occupy more heterogeneous habitat with lower jay activity than duller males. This age-and-plumage-structured settlement pattern is apparently maintained between years by the shifting of males into more preferred habitat as they become older. These observations are consistent with the hypothesis that habitat saturation, resulting in limited opportunities for recruitment into the breeding population, may have been an important factor in the evolution of delayed plumage maturation in this species.
Short Title:The Condor
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith