Dispersal and survival of kaki (Himantopus novaezelandiae) released in the Tasman River Valley, New Zealand
Cline, Geoffrey David
The release of captive-bred animals into specifically managed sites, such as predator-removal areas, is an increasingly utilized strategy to establish self-sustaining populations of endangered species. Nearly two decades of releases of captive-reared birds, in conjunction with intensive habitat management, have not led to delisting of the critically endangered New Zealand endemic black stilt, or kaki (Himantopus novaezealandiae). The kaki captive breeding facility at Twizel, central South Island, currently operates at full capacity each breeding season to maximize the number of young released into the wild. Current protocols require the release of two separate age cohorts to make available space for upcoming chicks. The need to release separate age cohorts may be a limiting factor for the Kaki Recovery Programme as the current recruitment rate for released birds to breeding age is low (28-29%) and survival in the initial post-release period for sub-adults is only (47-56%) and unknown for juveniles. Releasing the younger juvenile kaki may carry the risk of natural tendencies to disperse out of intensively managed areas. Thus survival could also be influenced by age at release and dispersal out of a predator-managed release site. This study investigated dispersal and survival of 29 juvenile and 22 sub-adult radio-tagged kaki in the first five months post-release from the predator-managed Tasman River Valley during the breeding season of 2005/2006. The following aims were defined: (1) investigate dispersal movements in relation to age at release, parent origin, and the proportion of time spent active; (2) calculate survival rates, risk ratios and explore differences in survival rates between age cohorts, and in relation to parent origin, proportions of time spent active, and dispersal from a predator-managed area. Radio-tracking indicated juveniles increased maximum distance from the release site significantly faster than sub-adults and the proportion of time birds spent active was positively correlated with maximum distance moved from the release site. Survival analysis indicated juveniles have lower survival than sub-adults, and regardless of age birds that remained in the Tasman River Valley have lower survival than birds that dispersed out of the predator-managed area. Although juveniles that disperse out of the Tasman River Valley have a lower risk of mortality events, they do not benefit the sub-population they were intended to augment. Releasing mixed age groups of birds at the same time of year will remove season as a factor and provide the opportunity to test further strategies to increase the success of future kaki reintroductions. Nevertheless, on the basis of the results of this study it is recommended that to maximize the success of future releases of kaki, managers should release only sub-adults as this age cohort appears more likely to remain in the vicinity of the release site and have a higher survival rate than that of juveniles, and thereby seem more likely to support the sub-population they are intended to augment.
Advisor: Seddon, Phil; van Heezik, Yolanda; Maloney, Richard
Degree Name: Master of Science
Degree Discipline: Zoology
Publisher: University of Otago
Research Type: Thesis
ix, 136 leaves :col. ill. ; 30 cm. Includes bibliographical references. University of Otago department: Zoology. "28 February, 2007"