Failure of translocated, captive-bred North Island weka Gallirallus australis greyi to establish at Karangahake Gorge, Waikato, New Zealand
Bramley G.N. & Veltman C.J. (1998) Failure of translocated, captive-bred North Island weka Gallirallus australis greyi to establish a new population. Bird Conservation International, 8, 195-204.
The weka Gallirallus australis is a large flightless rail endemic to New Zealand. The North Island subspecies G. a. greyi was formerly widespread, but now occurs only in the East Cape region of the mainland and on three small islands (two offshore and one in Lake Rotorua). Since 1960, a number of translocations of wild-caught weka have been attempted, but very few of these have resulted in the establishment of a persistent population. This study used radio-telemetry to monitor the fate of 17 captive-bred North Island weka released in an area of apparently suitable habitat at Karangahake Gorge (37º25' S, 175º44' E), near Paeroa, Waikato.
Release individuals were parent-reared in aviaries from stock from Kawau Island (36º25' S, 174º52' E) and a captive-breeding facility, both of which were originally derived from birds taken from the East Cape region of the North Island. Six individuals (all males) were over a year old when they were transferred to the aviary at the release site; the remainder were between 6-18 weeks old upon arrival and averaged 17 weeks old at release. Individuals spent on average eight weeks in the release aviary prior to release.
A total of 17 individuals (four females and 13 males) were released, in groups of 2-6, on five dates between October 1992 and March 1993. All individuals were ringed with a numbered metal ring and at least one coloured plastic ring, and 10 birds (four females and six males) were also fitted with back-mounted radio-transmitters. Supplementary food was made available after release until the end of the study.
The location of radio-tagged birds was checked at 12-hour intervals for two days following release, and then at randomly selected times during monthly visits of four to seven days between November 1992 and June 1993. Between five and 24 independent point locations were obtained for each radio-tagged individual. Opportunistic observations were also made of non-tagged birds.
Of the 10 radio-tagged weka, seven were killed by dogs Canis familiaris, one was killed by a ferret Mustela putorius, one died of unknown causes, and one slipped its radio-transmitter and its fate remained unknown. Overall, only one of the 17 individuals released during the study survived until 242 days after release; 12 birds survived fewer than 50 days. There was no significant difference in the rate of disappearance of radio-tagged birds compared with those not carrying radio-transmitters. Radio-tagged weka had small home ranges (average: 2.7 ha; estimated using the minimum convex polygon method), and dispersed c.1,270 m on average (range: 134-10,000 m) during the study.
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