Comparative studies of nest predation and identification of nest predators promote understanding of the selective environment that shapes avian life histories. Due to the low diversity of native mammalian and reptilian predators on oceanic islands, insular forest birds are assumed to incur lower nest predation rates than related continental species. We studied correlates of nest predation in insular and continental subspecies of Rufous Fantail (Rhipidura rufifrons) found on the island of Rota and in eastern Australia. Overall, daily survival rate (DSR) was similar between study sites, but egg stage DSR (laying and incubation) was higher in Australia than on Rota while nestling stage DSR was higher on Rota than in Australia. DSR was negatively related to nest age in Australia and the magnitude of this relationship varied by year. On Rota, DSR was higher in the nestling stage than during the egg stage and also higher on our study plot where Mariana Crows (Corvus kubaryi)—the principal nest predator—were less common. Although climate variables did not predict DSR at either site, in Australia, lace monitors (Varanus varius) were more likely to prey upon nests on days without rain. Lace monitors also tended to prey upon nests late in the nestling stage, which likely contributed to the decline of DSR with age. Our results suggest that life history variation between continental and insular birds may be explained, in part, by differences in age-dependent DSR due to the reduced diversity of certain predator guilds on oceanic islands. Therefore, consideration of the nest predator community and age-dependent nest predation risk could help explain additional life history variation in comparative studies.
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Vol. 135 • No. 4