kokako

The theory of population regulation predicts that threatened species are safest at high population numbers, partly because density-dependent compensatory mechanisms counteract unpredictable disturbances. We illustrate this principle using data from the endemic kokako (Callaeas cinerea wilsoni) populations in the North Island, New Zealand. First we calculate the fledging rate per female (production) necessary to stabilise the population and thereby the residual numbers of nest predators, namely ship rats and possums, which have to be achieved to reach this production.

Expenditure on endangered species management is increasing greatly, on a global basis. Managers need tools to evaluate the performance of endangered species programmes because there will always be more demand for resources than there are available. Cost Effectiveness Analysis (CEA) is used here to evaluate the performance of the kokako (Callaeas cinerea) recovery programme. This species is being managed at a number of sites in New Zealand and analysis shows a large variation in costs and effectiveness between these sites.

Populations of four species of carnivores were sampled over the five years 1983-87 at Pureora Forest Park, by regular three- monthly Fenn trap index lines supplemented with occasional control campaigns by shooting and additional traps. Stoats were the most frequently collected (63 captures), followed by weasels (18), cats (15) and ferrets (13). Stoats ranged throughout the mosaic of forest types but especially the older exotic blocks, hunting rabbits, rats, possums and birds. The mean age of 55 stoats trapped was 15 months, and their maximum life span about 5 years.

Populations of ship rats (Rattus rattus), Norway rats (R. norvegicus), feral house mice (Mus musculus), stoats (Mustela erminea), weasels (M. nivalis), and ferrets (M. furo) were sampled with killtraps every three months from November 1982 to November 1987 in logged and unlogged native forest and in exotic plantations of various ages at Pureora Forest Park, central North Island. Mice (n=522 collected) were fewest in unlogged native forest, more abundant in road edge cutover forest, and most abundant in a young (5-10 year old) plantation.