BiologyBiology

Biology

The Christmas Island Goshawk has been recorded eating a wide range of vertebrates and invertebrates including birds, small mammals and insects. Prey includes Christmas Island White-eye Zosterops natalis, Island Thrush Turdus poliocephalus, Emerald Dove Chalcophaps indica, Java Sparrow Lonchura oryzivora, domestic chickens Gallus gallus, (Lister 1888, Gibson-Hill 1947, Hill, unpubl. data); as well as nestling Red-footed Boobies Sula sula (Hill, unpubl. data) and an adult Golden Bosun Phaethon rubricauda westralis (J. Tranter pers. comm.). It has also been recorded catching rats Rattus rattus (Gibson-Hill 1947) and ‘lizards’ (Lister 1888). It is frequently seen catching grasshoppers (probably Valanga sp.) which are common in secondary vegetation around the island (Gibson-Hill 1947, Hill unpubl. data). Gibson-Hill (1947) also recorded it feeding on the large centipede Scolopendra morsitans, which is widespread on the island, and on beetles (Coleoptera) and mantids (Mantidae).

The Christmas Island Goshawk captures its prey off the ground or in the air by seizing it in flight with its long, strong legs. Like other goshawks, it will hunt from a perch where it may sit for some time waiting for suitable prey. Christmas Island Goshawks will chase small flying birds through the forest as well as pounce on birds foraging on the ground (Hill unpubl. data). Hill observed goshawks ‘short-stay perch-hunting’ (after Newton 1986) flying along a track, perching for a few minutes then flying 50-100m further and landing again, as well as pursuing insects on the ground and snatching insects off foliage. There is likely to be some sex differences in hunting and in diet, as is found in both Brown and Grey Goshawks (Marchant & Higgins 1993). Given the large sexual dimorphism (similar to Grey Goshawk, Hill unpubl. data) and the opportunity for niche expansion on the island in the absence of other diurnal raptors, this difference may be quite pronounced.

Gibson-Hill (1947) described three Christmas Island Goshawk nests all of which were in near-horizontal forks of forest trees, one 10m high and two 15-20m in tall forest trees. Hill (unpubl. data) observed four nests: two in Syzygium nervosum in Primary rainforest; and two in Terminalia catappa in Marginal rainforest. All nests were 25-35m above the ground, in the fork of two or more branches, three towards the edge of the crown, and one in the middle of the tree. One nest (probably not used) was 30-40cm in diameter, two others were 50-80cm in diameter, and the fourth was under construction. Nest size and location within the tree share more similarities with Grey than Brown Goshawks (J. Young pers. comm.; see Burton et al. 1994).