Wandering stars: age-related habitat use and dispersal of Javan Hawk-eagles (Spizaetus bartelsi)

Abstract

Natal dispersal and philopatry have rarely been studied in tropical forest raptors. Especially with respect to endangered species with fragmented distributions more knowledge of dispersal and age-related habitat preferences is needed for proper management. We conducted an island-wide study on age-related habitat preferences of the endangered Javan Hawk-eagle (Spizaetus bartelsi), Indonesia's national bird. The Javan Hawk-eagle is a true forest eagle, but is occasionally observed in non-forested areas. On the basis of 95 visual encounters in 50 localities in the period 1980–2002, we established that there were no age-related differences in geographical, altitudinal or climatic distribution. In habitat preferences, however, juveniles and immatures are proportionally more often recorded in open and disturbed habitats than adults, which seem to have a greater preference for evergreen forest. These results indicate that the prime habitat for adult Javan Hawk-eagles is evergreen forest and to a lesser degree secondary forest, with juveniles dispersing out of their natal territory into different habitat types, including seemingly unsuitable types. In their habitat choice, immatures tend to be more similar to adults than to juveniles, which is an indication that their dispersal takes place into habitats that are more suitable for establishing a breeding territory.