The ecology of the kākerōri (Rarotonga flycatcher) Pomarea dimidiata, with special reference to fledged young : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Ecology at Massey University

Abstract

The Kakerori (Pomarea dimidiata) is a small flycatcher, endemic to Rarotonga in the Cook Islands. In August 1991 the total world population was estimated at 47 individuals, an increase of 14 birds from the previous year. Kakerori live in the forest canopy of small valleys in the steep, mountainous interior. This study concentrated on the ecology of young birds and factors affecting the breeding success (the number of fledged young produced) of pairs. Young birds remain in the parental territory for up to four months after fledging, where they are commonly found high in the leafy canopy (mean = 25.7m n=36). After parental care has ceased, young birds move to the high, exposed ridges up to 100m from their natal territories (mean = 87m n=14), and remain on average, 2.4m (n=14) from the ground. Successful Kakerori territories (those that have produced fledged young) have a relatively lowered canopy (10.3m) and few ferns (28.3%), with many juvenile trees (38.3%) and shrubs (33.4%) making up the shrub layer. These juvenile trees may ensure a continued closed canopy. Successful territories also have few, large trees (mean total basal area = 7.39m2) and a higher level of moss (16.5%) which may encourage larger populations of insects as well as providing possible nest sites for Kakerori. Unsuccessful territories (those that produced no fledged young) have many, immature trees (mean total basal area = 3.21 m2) and little moss (8.1%). In general, insect numbers varied little between successful and unsuccessful territories, however during February 1991 successful territories had a large percentage of flies (40.4% n=23) compared to unsuccessful (8.3% n=2). During February when adults are feeding newly fledged young, a greater availability of insects may positively affect breeding success. Poison baits for rats have been laid in the study area since 1988 and the number of fledged young found has increased from one in 1987/1988 to 14 in 1990/1991. The most effective method of conserving the Kakerori may be to continue indefinitely the rat-baiting campaign throughout the study area and neighbouring valleys. This would depend entirely on the availability of funds and committed personnel.