Abstract
In long-lived species, the age-, stage- and/or sex-dependent patterns of survival and reproduction determine the evolution of life history strategies, the shape of the reproductive value, and ultimately population dynamics. We evaluate the combined effects of age and sex in recruitment, breeder survival and breeding success of the globally endangered Egyptian vulture (Neophron percnopterus), using 31-years of exhaustive data on marked individuals in Spain. Mean age of first reproduction was 7-yrs for both sexes, but females showed an earlier median and a larger variance than males. We found an age-related improvement in breeding success at the population level responding to the selective appearance and disappearance of phenotypes of different quality but unrelated to within-individual aging effects. Old males (≥8 yrs) showed a higher survival than both young males (≤7 yrs) and females, these later in turn not showing aging effects. Evolutionary trade-offs between age of recruitment and fitness (probably related to costs of territory acquisition and defense) as well as human-related mortality may explain these findings. Sex- and age-related differences in foraging strategies and susceptibility to toxics could be behind the relatively low survival of females and young males, adding a new concern for the conservation of this endangered species.
Highlights
Dimorphic species with asymmetric parental roles[13]
Female and male Egyptian vultures showed a median age of first reproduction of 6 and
Our results strengthen the importance of taking into account age and sex when studying life histories, even among monogamous species in which both sexes exhibit similar parental care[1,2,9,11,29]
Summary
Dimorphic species with asymmetric parental roles[13]. sex-specific life-histories exist even in monogamous species with low sexual body-size dimorphism and similar parental investment in reproduction[9,11]. Large avian scavengers (vultures and condors, Accipitridae and Cathartidae, respectively) are among the longest-lived vertebrates, with some individuals living over 40 years[22] These species show delayed maturity such that individuals typically do not recruit into the breeding populations until they have at least acquired adult plumage patterns after several years of life[23] Among long-lived territorial species it is very difficult to achieve large sample sizes of known-age marked birds for long time periods (as that obtained for short lived and/or colonial species)[11], which precludes an examination of how aging affects individual life-history strategies For this reason, potential sex-specific trade-offs between recruitment, breeding success and/or survival remain understudied[26]. Since the parental roles of Egyptian vultures are roughly similar between sexes (see below), we expect similar parameters for males and females and/or age related improvements early in life (through acquisition of skills and experience or the (dis)appearance of different quality phenotypes) and/or late-in-life deteriorations due to senescence
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