2000 Volume 32 Issue 1 Pages 13-23
It has been inferred that the population of Bull-headed Shrikes, Lanius bucephalus, increased rapidly on Minami-daito Island, Japan, beginning in 1973-74. This isolated population on a remote island in the Pacific Ocean is about 500km away from the previous southern limit of the breeding area of this species. The plumage and external morphological characteristics of the Minami-daito Bull-headed Shrikes are described, and the results of an investigation into the distribution, sex ratio, and breeding ecology of the population made from January to February and from April to May 1998, are discussed. As there have been previous reports of hybrids between the Bull-headed Shrike and the L. cristatus lucionensis subspecies of the Brown Shrike (a summer migrant to Japan), the characteristics of the Bull-headed Shrikes currently on Minami-daito were compared with those of both L. c. superciliosus and L. c. lucionensis. The Minami-daito Bull-headed Shrikes were found not to show either plumage or external morphological characteristics typical of L. c. lucionensis. Shrikes were observed in all of the typical habitats on the island, at a rate of 2.1 males per km and 1.6 females per km. Most nests were built in Calophyllum inophyllum, and the mean nest height above ground was 252cm. Egg laying was observed for the first time in late January, and continued until April. It was not possible to determine whether or not shrikes continued to lay after May.
