BREEDING BIOLOGY DURING ESTABLISHMENT OF A REINTRODUCED GRIFFON VULTURE GYPS FULVUS POPULATION

We studied the breeding parameters of a reintroduced population of ind ividually marked Griffon Vultures Gyps fulvus in the Grand Causses reg ion of southern France from the time of first reintroduction in 1982 t o 1992. Among nesters, 65% of the birds released as immatures or born in the wild recruited into the breeding population when 4 years old, i ,e. 1 year earlier than previously described. The proportion of birds nesting each year was relatively high and increased with time, suggest ing that conspecific attraction favoured recruitment. We detected a pe rmanent adverse effect of long-term captivity on the nesting success o f birds released when more than 2 years old: compared to the natural p opulation, birds which had been kept in captivity showed a reduced bre eding success during the whole study period, The breeding success of r eleased immatures and wild-born birds was similar to the highest value s observed in a natural population in the Spanish and French Pyrenees. Breeding failures did not usually result in mate change but affected nest-site fidelity, Birds not born in the wild were more likely to rec ruit to the largest subcolonies available, which highlights the role o f social attraction. The observed philopatry of wild-born birds probab ly resulted from such a social attraction since most of them were born in the largest subcolony. Conspecific attraction maintained the spati al aggregation of nests, whereas nest changes after a breeding failure favoured the spatial expansion of the colony.