Spatial patterns of the Ryukyu Scops Owl’s Otus elegans breeding success and forest landscape factors on Amami-Ōshima Island

Abstract

We conducted route censuses of the near threatened Ryukyu Scops Owls Otus elegans throughout forest areas on Amami-Oshima Island, including mature and secondary broad-leaved forests during the breeding season of 2017. A total of 98 fledglings were detected at 58 points during censuses conducted from 27 June to 25 July; fledglings were detected on more than one day at 13 of these points. We tested a GLMM model with detection/non-detection as a categorical response variable for 53 fledgling detection points and 54 non-detection points randomly located along the individual census routes at approximately the same rate as the detection points. Five explanatory variables were examined: area of forest vegetation (evergreen broad-leaved, secondary evergreen broad-leaved, secondary conifer or secondary deciduous broad-leaved), area of open land, length of forest edge, distance from residential area, and elevation. The model showed a high explanatory power, when it included variables for the area of evergreen broad-leaved forest (positive effect), probably because mature subtropical evergreen broad-leaved forest contains more old trees with cavities suitable for nesting in by O. elegans.