Abstract
The status of the isolated Ryukyu Robin Erithacus komadori population in the Danjo Islands and its molecular phylogenetic position were investigated from 2003 to 2006. Point count and playback methods were simultaneously used to determine the territory density in mature forests on O-shima and Me-shima, the two largest of the Danjo Islands. The territory densities (0.4–0.5/ha on O-shima and 0.4/ha on Me-shima) were considerably lower than in the 1970s and 1980s. Increased predator populations resulting from human activities, as well as forest degradation caused by rare and severe natural disturbances are likely to be the main causes of the decline of this bird. Two adult males caught on O-shima had similar measurement values and feather coloration to those in the Tokara and Amami Islands. They had the same mtDNA control region haplotype unique to the Danjo Islands, and the haplotype was classified into the northern subspecies E. komadori komadori clade in the maximum-likelihood tree. The pairwise differences among populations within the northern subspecies clade were much smaller (K-2p distances; 0.0054–0.0064) compared to those between subspecies. Therefore, population expansion or habitat fragmentation causing the present level of isolation is thought to have happened much later than subspecific diversification.
