Bruce Byers

Song Types, repertories and son variability in a population of Chestnut-Sided Warblers

Bruce Byers — Thu, 08 Mar 2012 06:12:05 PST

Geographic Variation of Song Form within and among Chestnut-Sided Warbler Populations

Bruce Byers — Thu, 08 Mar 2012 06:07:26 PST

Extrapair Paternity Increases Variability IN Male Reproductive Success in the Chestnut-Sided Warbler (Dendroica Pensylvanica), A Socially Monogamous Songbirds

Bruce Byers — Thu, 08 Mar 2012 06:02:12 PST

A monogamous mating system that includes extrapair fertilization can potentially generate higher variability in male reproductive success than monogamy without extrapair fertilization. That increased variability could provide a correspondingly higher opportunity for sexual selection and, thus, for the origin and persistence of sexual dimorphism in monogamous species. To determine whether extrapair fertilization enhanced the opportunity for sexual selection in a sexually dimorphic, monogamous bird species, we used microsatellite DNA typing to assess the prevalence of extrapair fertilization and its effect on variation in male reproductive success in a population of Chestnut-sided Warblers (Dendroica pensylvanica). We found that the level of extrapair fertilization in our study population was at the upper end of the range reported for bird populations (47% of nestlings had extrapair fathers; 61% of broods contained extrapair offspring). We also discovered that almost all extrapair offspring were sired by paired males resident on nearby territories. In addition, we found that variation in male reproductive success was substantially higher than variation in female reproductive success, and that extrapair fertilizations made a significant contribution to variation in male reproductive success. Together, those findings suggest that extrapair fertilization creates an opportunity for sexual selection on male traits in this population.

Extrapair paternity in chestnut-sided warblers is correlated with consistent vocal performance

Bruce Byers — Thu, 08 Mar 2012 05:52:10 PST

The elaborateness of many bird songs is commonly presumed to have evolved under the influence of sexual selection by female mate choice. Thus, aspects of acoustic diversity, such as song repertoire size, are seen as likely targets of female choice. In many songbird species with song repertoires, however, the repertoires are small. In such species, female choice might be based on song features other than, or in addition to, song diversity. To investigate this conjecture, I assessed singing and paternity in a population of chestnut-sided warblers (Dendroica pensylvanica), a species in which song repertoires are of modest size. Twenty-two song traits were evaluated to determine which ones best predicted male extrapair reproductive success. The candidate traits encompassed measures of song diversity (e.g., song repertoire size), gross-scale song performance (e.g., singing rate), and fine-scale song performance (e.g., variability among songs in a bout). Regression analysis revealed that the best predictor of extrapair success was singing with little variability. In particular, the most successful males sang with consistent pitch and timing, as well as high pitch. The greater extrapair success of males with more consistent vocal performance may be due to female preference for such performance, which could be an indicator of male quality.