Some songbird parents might improve their own fitness by manipulating their offspring into leaving the nest early, at the cost of fledgling survival, a study finds. Young birds that prolong their stay in the nest increase their chances of survival. However, continuing care may impose an overall cost on parents by decreasing the fitness of the entire brood. The influence of this kind of parent-offspring conflict on the age at which songbirds fledge, or leave the nest, is unclear. Todd Jones and colleagues analyzed data from eight studies of 18 songbird species across the United States. Twelve of the species showed evidence of postfledging bottlenecks; in these species, the mortality rates of fledglings were higher than those of nestlings. Postfledging bottlenecks led to a 14% increase in the probability that at least one offspring in the brood would survive until independence. Moreover, parental benefits associated with early fledging could explain variation in fledging age across species. Together, the findings suggest that songbird parents enhance their own fitness by manipulating offspring into fledging early--at the cost of the fledglings' survival. According to the authors, the findings suggest that parent-offspring conflict might similarly affect the age of offspring during key transitions in life for other animals that provide parental care.
Article #20-08955: "Parental benefits and offspring costs reflect parent-offspring conflict over the age of fledging among songbirds," by Todd Jones et al.
MEDIA CONTACTS: Todd Jones, University of Illinois at Urbana-Champaign, IL; tel: 614-886-4241; e-mail: toddmj@illinois.edu ; Michael Ward, University of Illinois at Urbana-Champaign, IL; tel: 217-244-4089; e-mail: mpward@illinois.edu
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Proceedings of the National Academy of Sciences