Apparent Annual Survival Rates of Male Ryukyu Scops Owls on Eight Islands in the Ryukyu Archipelago

We aimed to calculate the annual survival rates of male Ryukyu Scops Owl Otus elegans on eight islands, Nakano-shima (NKN), Amami-oshima (AMM), Tokuno-shima (TKN), Izena (IZN), Iheya (IHY), Ishigaki (ISG), Iriomote (IRO) and Hateruma (HTR), in the Ryukyu Archipelago, and to discuss the environmental factors that cause differences in their annual survival rates. A total of 111 owls was marked (19 on NKN, 19 on AMM, 11 on TKN, seven on IHY, four and six on IZN, 14 on ISG, 20 on IRO and 11 on HTR) between March and July from 2011 to 2016. We investigated whether they were resighted at the same sites at different annual intervals on each island in February, June-October, and December from 2016 to 2023. To calculate survival rates from unequal interval observations, we used a model that relaxed the assumptions of the Cormack-Jolly-Seber model, which calculates survival rates from equal intervals. The mean annual survival rate for all eight islands was 80.1% with a credible interval of 68.0% to 91.7%. The mean annual survival rates for IHY (87.0%), AMM (79.8%) and NKN (88.2%) were within the credible interval for the mean survival rate for all islands, although the credible interval for IHY tended to be larger than that for the other two islands. The annual survival rates for IZN (50.2%) and TKN (49.9%) were remarkably lower than those for the other six islands, although with very large credible intervals. The mean annual survival rate for HTR (96.3%), IRO (91.5%) and ISG (97.9%) tended to be high compared to that for all the other islands. Estimates of annual survival indicate that there may be differences in owl survival rates between islands. The results suggest that annual survival rates vary depending on island environments. This study highlights the biological evolutionary importance of comparing differences in traits of Ryukyu Scops Owl among islands.