The main prey of Brown Hawk-Owl Ninox scutulata japonica during the breeding season consists of Coleoptera, although Lepidoptera are also delivered frequently to nestlings during the early nestling period. Changes in the frequency of food items delivered during the nestling period are unclear because Brown Hawk-Owl forage for insects at night. To evaluate how prey abundance in the nesting territory affects changes in the frequency of delivery of Coleoptera and Lepidoptera to nestlings, we collected prey remains around the nest site, and surveyed the amount of insects consumed as the main prey of the Brown Hawk-Owl. In order to be able to discuss the characteristics of feeding ecology, we also investigated the body parts of insects that Brown Hawk-Owls delivered to their nest. Although there were fewer individual Lepidoptera than Coleoptera within the territory of the owls, adult owls frequently delivered Lepidoptera to their chicks until the middle of the nestling period. Brown Hawk-Owls then switched their main prey from Lepidoptera to Coleoptera, according to the abundance of insects within their territory, towards the end of the nestling period. These results suggest that Brown Hawk-Owls selectively delivered Lepidoptera to their nestlings until the middle of the nestling period, but that this selectivity disappeared toward the end of the nestling period. Heads, thoraxes, and abdomens of Lepidoptera, and abdomens of Coleoptera were delivered frequently to nestlings suggesting that Brown Hawk-Owls may select soft exoskeletons of Lepidoptera and Coleoptera due to the undeveloped digestive organs of their chicks. To understand the species-specific feeding ecology of the Brown Hawk-Owl, we should investigate the species' feeding pattern in relation to the development of the digestive organs of the nestlings.
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