Reverse Mounting in Vultures: A Sexual Tutoring Hypothesis

Mating performance requires complex motor skills and inter-individual synchronization, yet the developmental pathways of copulatory competency remain poorly understood. Reverse mounting, where females mount males, is integrated into the behavioural toolkits of various monomorphic, long-lived birds, but its adaptive function remains debated. Using a 35-year demographic dataset of a wild griffon vulture (Gyps fulvus) population, we tested whether reverse mounting functions as a mechanism of 'sexual tutoring' during early reproductive life. Longitudinal observations of individuals marked as nestlings (n = 455) and tracked through their reproductive stage revealed that, out of 1498 total observed copulations for them, 1.5% corresponding to 23 cases were reverse copulations involving 9 marked individuals of known exact age. Reverse mounting showed a significant decrease with age, being concentrated in earlier stages with a mean age of 7 years, where 95.7% of these interactions featured an adult female paired with a younger male, and virtually disappearing by 12 years of age with the exception of a single record involving a 25-year-old individual. Subadult females-on-adult males mounting was never observed. While breeding attempts featuring observed reverse copulations showed reduced laying probability, final breeding success was correlated with the individual's chronological age rather than the behaviour itself. Our findings provide correlational evidence consistent with the hypothesis that reverse mounting may act as a socially mediated learning process. In large-bodied, monomorphic species with high mate fidelity, experienced partners could mitigate asymmetric skills by tutoring youth, potentially accelerating the acquisition of necessary copulatory dexterity.