Breeding timing and nest predation rate of sympatric scops owls with different dietary niche breadth

Breeding timing is one of the key life-history traits considered to be under strong stabilizing selection, such that offspring should be born when food resources are most abundant. Predation, however, may also affect the breeding timing because nest predationis a leading mortality for many species, although this possibility has been less considered. Here, we examined the possible effects of nest predationon breeding timing by comparing sympatric scops owls in a subtropical forest where only reptilian predatorsare present. The Japanese Scops Owl ( Otus semitorquesTemminck and Schlegel, 1844), a dietary generalist, bred one month earlier than the specialist Ryukyu Scops Owl ( Otus elegans(Cassin, 1852)). The breeding timing of the Ryukyu Scops Owl matched with the emergence of their main prey species, but also matched with predatoractivity. Accordingly, the predationrate on eggs or nestlings was 7.5 times higher in the Ryukyu Scops Owl (13.9%; 21 out of 150 nests) than in the Japanese Scops Owl (1.9%; ...