ORIGINAL PAPER Parental conflict and brood desertion by females in blue-headed vireos Eugene S. Morton & Bridget J. M. Stutchbury & Ioana Chiver Received: 15 October 2009 / Revised: 6 January 2010 / Accepted: 20 January 2010 / Published online: 24 February 2010 # Springer-Verlag 2010 Abstract We investigated sexual conflict over parental care in blue-headed vireos (Vireo solitarius) and documented the first example of unvarying unisexual brood desertion in passerines. Females at all nests (N =24) that were monitored closely near fledgling, deserted their broods on or near the day of fledging leaving males alone to complete parental care of young. No males deserted. This observational evidence was confirmed with radiotracking of females (2004, 2007) and both pair members (2008). Radiotracked females began visiting distant males 1–4 days before young left the nest, subsequently paired with males 355–802 m away, and laid first eggs in new nests less than 5 days after deserting. In contrast, females suffering nest predation did not desert and renested with the same male. We suggest equal parental care (nest building, incubation, feeding) in the sexes, genetic monogamy, and an adult sex ratio biased towards males has led to female control of brood desertion in this species. Unisexual desertion may be more important in altricial birds than generally realized and we discuss prerequisites to predict its occurrence. One is genetic monogamy, which may be a female tactic that reduces the likelihood of males evolving counter-adaptations to female desertion. Keywords Offspring desertion . Genetic monogamy . Sexual conflict . Sequential polygamy . Parental investment . Altricial young . Vireo solitarius . Blue-headed vireo Introduction Sexual conflict, an evolutionary contest over reproduction resulting from gender differences in the comparative value of current and future reproductive investment, has been documented in a variety of insects, fish, amphibians, birds, and mammals (Parker 1979; Arnqvist and Rowe 2005). An extreme result of sexual conflict known for several species of birds, offspring desertion, occurs in species where both parents care for the young but where one pair member leaves parental care entirely in the hands of its mate (deserts) (e.g., Beissinger 1990; Franz 1991; Griggio et al. 2004; Pogány et al. 2008; Székely 1996; Székely et al. 1996). The social dynamics of brood desertion, including which individual or gender deserts first, has become a focus for the study of sexual conflict in birds (reviewed in Hartley and Royle 2007; Olson et al. 2008). Although better developed for insects (Arnqvist and Rowe 2005), sexual conflict in birds has produced several theoretical predictions. For example, sexual conflict over brood desertion should be lower in altricial species compared to species with precocial young because altricial young are so demanding of parental care (Olson et al. 2008). But, even with the higher demand for parental care, mate desertion by either sex has been documented in altricial species even though a deserter risks lowering its reproductive success if the remaining parent cannot Communicated by R. Gibson Electronic supplementary material The online version of this article (doi:10.1007/s00265-010-0910-7) contains supplementary material, which is available to authorized users. E. S. Morton (*) Hemlock Hill Field Station, 22318 Teepleville Flats Road, Cambridge Springs, PA 16403, USA e-mail: mortone@si.edu B. J. M. Stutchbury : I. Chiver Department of Biology, York University, Toronto, Ontario M3J 1P3, Canada Behav Ecol Sociobiol (2010) 64:947–954 DOI 10.1007/s00265-010-0910-7