Nest success and life history syndromes of island and continental Rufous Fantail (Rhipidura rufifrons) subspecies

Abstract

Insular avian species are predicted to have slower life history syndromes than related continental species, due to lower predator diversity on oceanic islands. However, detailed studies of nest predation, life history and behavior of related oceanic island and continental taxa are lacking. I studied Rufous Fantail (Rhipidura rufifrons) life history traits in New South Wales, Australia and on the oceanic island of Rota, Commonwealth of the Northern Mariana Islands. Average daily survival rate (DSR) of nests was similar between sites, but this owed to a disordinal interaction between site and nest age. DSR was negatively related to nest age in Australia, likely because nest predation by reptiles usually occurred late in the nestling stage. By contrast, DSR was higher in the nestling stage than the egg stage on Rota. Nest site characteristics were unrelated to DSR at both sites and nest fate was not repeatable when fantails reused nest sites for multiple clutches. Therefore, nest predation may occur incidentally, rather than due to intrinsic differences in nest site quality. As expected, insular fantails had a slower life history syndrome: fantails on Rota had longer nestling development periods, higher nestling provisioning rates and slower growth of nestling locomotor traits. At both sites, nest guarding effort decreased with increasing nestling provisioning rate, suggesting a trade-off between these activities. However, regardless of provisioning rate, fantails spent more time guarding their nests on Rota than in Australia. I could not compare adult survival between study sites because color bands caused leg injuries on Rota, while I did not observe band-related injuries in Australia. Site-specific differences in the prevalence of band-related injuries may reflect variation in the frequency with which fantails encounter spider webs, since injuries were caused by spider web accumulation under the bands. Overall, my results suggest that one causal explanation for life history differences between continental and insular birds is variation in age-dependent DSR due to reduced predator diversity on oceanic islands. Additionally, increased investment in offspring and slower development of nestling locomotor traits may explain some of the vulnerability of insular birds to the introduction of non-native predators.