Asymmetrical Parental Investment Across Breeding Stages in the Globally Endangered Egyptian Vulture (Neophron percnopterus) in Nepal.

Understanding sex-specific parental roles is critical for interpreting reproductive strategies in long-lived, monogamous birds with low fecundity. Birds of prey often exhibit asymmetric biparental care; however, empirical evidence from South Asia, mainly on Neophron percnopterus ginginianus sub-species remains limited. We investigated breeding phenology and sex-specific parental investment between 2021 and 2024, across breeding stages of the globally endangered Egyptian Vulture, Neophron percnopterus ginginianus, in the Kaski district, which supports a high density of the species' breeding population. We monitored 46 breeding attempts to document breeding phenology and conducted behavioral observations at 38 unique breeding attempts from 17 nests, comprising 20 nest-building, 18 incubation, and 18 chick-rearing attempts. Using generalized linear mixed-effects models and an information-theoretic model-selection approach, we evaluated sex-specific parental investment and the influence of offspring development and environmental conditions on breeding behavior. Breeding onset varied among nests and years, with nest-building occurring predominantly in March, and the overall breeding cycle lasted approximately 18.4 weeks. Egyptian Vultures exhibited bi-parental care throughout the breeding cycle, but parental roles were asymmetric and varied among stages. Males delivered nesting materials more frequently than females, whereas females contributed more to nesting material maintenance. During incubation, both sexes contributed similarly to incubation effort, while incubation bout duration decreased with increasing sunlight exposure. During chick-rearing, females were most likely to attend and spent longer duration at nests and feeding chicks when present, whereas males delivered more food more frequently. Food provisioning rate increased with chick age, whereas feeding duration decreased with increasing precipitation. Chick became increasingly independent as they developed, with the probability of self-feeding increasing with chick age. Aggression by chicks toward parents also increased with chick age and was directed predominantly toward females. Overall, our findings reveal complementary and stage-dependent parental roles in Egyptian Vultures, with males contributing more strongly to resource acquisition and females investing more in direct offspring care. These findings provide detailed evidence of how parental roles shift across the breeding cycle and offer region-specific insights into the reproductive ecology of this globally endangered scavenger.