Reintroduction of Juvenile Black Stilts to the Wild.
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
Black stilts (Himantopus novaezelandiae) are an endangered wader endemic to New Zealand. The black stilt population is critically low and managers are trying to return the species to a sustainable level by captive-rearing young stilts from eggs. A new and experimental reintroduction programme began in 1993. Over two years, 57 young birds were released to the wild within their natural range in the Mackenzie Basin. The area they were initially released into contains a diversity of feeding habitats and mammalian predators are excluded. Newly released stilts remain around the release area for the first two months feeding and roosting within the predator-reduced area. Many bird species in nature have a high mortality during their juvenile stage. Survival rate of released juvenile black stilts was approximately 50% for the first four months and 30% after the first year. Of the birds whose bodies were found, most had died from trauma related injuries. The causes of the injuries are not known, but several hypotheses have been proposed. Signs on the bodies indicate the causes of death include predation, internal parasites, infection, thyroid dysplasia and powerlines strikes. Time budget and foraging samples were collected over the first four months following the 1993 spring release, periodically over the subsequent over winter, and the first four months following the 1994 spring release. This study investigated possible causes of death of stilts by comparing behaviours of birds that eventually live with those that eventually die. From these comparisons no differences were found in the behaviour of the two groups. Results indicate that all stilts are equally prepared at release and causes of death are independent of the bird's behaviour. Alternative release areas are suggested for future black stilt reintroductions as a means of reducing the initial mortality. The rate of, mortality observed in newly released stilts is likely to be associated with captive-rearing. However, causes and rates of mortality in older captive-reared birds are likely to approximate wild birds of similar age.