Double-nesting behaviour and sexual differences in breeding success in wild Red-legged Partridges Alectoris rufa

Double-nesting behaviour, a rare breeding system in which females lay in two nests, one incubated by herself and the other one by her mate, could be considered an intermediate stage in the evolutionary trend from biparental to uniparental care of single clutches. We examined the occurrence and success of double-nesting behaviour in Red-legged Partridges Alectoris rufa in Central Spain. Clutch size and hatching success were recorded, as well as the variation in these between years and between incubating sexes. Participation in incubation was higher for females (94.76%) than males (41.0%), and the proportion of incubating males varied markedly between years, with no incubating males in one dry year and approximately 50% of males incubating in other years. There was significant variation among years and between sexes in laying date, clutch size and hatching success. Clutch size decreased with later laying date in males and females. The probability of clutch loss to predation differed between sexes, being much higher for nests incubated by females. Our results suggest that both rainfall and predation influence the occurrence and success of double-nesting.