Nest defense and parental investment in Song Sparrows (Melospiza melodia)

Individual variation in nest defense behaviour is common in altricial birds, but despite clear predictions about why such variation exists there is no consensus on its causes. We tested for an influence of five predictors of individual variation in nest defense behaviour, including time of season, offspring age, parental age and sex, and clutch size in a well-studied Song Sparrow (Melospiza melodia (Wilson, 1810)) population. We recorded parental responses to a standardized human approach and used model selection to assess support for each predictor. Parents tended to approach observers less closely and alarm-call less as the breeding season progressed, indicating a modest seasonal decline in parental nest defense, consistent with the hypothesis that the reproductive value of offspring influenced parental defense behaviour. Clutch size effect estimates were insignificant, but it was weakly supported as a predictor of nest defense, as expected if parental investment in defense and current reproductive effort are positively related. Offspring age, and parental age and sex received little or no support as affecting parent nest defense. Our results offer limited support for the hypothesis that the reproductive value of offspring affects parental nest defense.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author