Arboreal nesting and utilization of open-cup bird nests by introduced Ship Rats Rattus rattus on an oceanic island

The introduction of exotic rats Rattus spp. is one of the most important factors contributing to the reduction in avian diversity and extinctions on oceanic islands. However, little is known about factors other than predation, which are associated with the loss of island biodiversity. We report that introduced Ship Rats Rattus rattus constructed arboreal dome-shaped nests and secondarily used open-cup nests of the Bull-headed Shrike Lanius bucephalus for roosting or rearing young in trees within hedgerows along sugarcane fields of Minami-daito Island (northwest Pacific). We found that temporal nest utilization by Ship Rats forced Bull-headed Shrikes to abandon their nests before egg-laying. We suggest that kleptoparasitism applies to the interaction between Bull-headed Shrikes and Ship Rats, which usurp shrike nests during their breeding period. It is necessary to consider the potential effects of introduced Ship Rats on insular avian communities not only through predation but also through interspecific interaction over nest-sites.