Productivity of kakapo (Strigops habroptilus) on offshore island refuges

The reproduction of kakapo (Strigops habroptilus) on offshore island refuges was monitored between 1990 and 2002. Productivity was primarily determined by the proportion of females that nested each breeding year. Within the same island, the proportion of females nesting each breeding year ranged between 33 – 95% but, as a proportion of the total female population, was just 5 – 42% between 1990 and 1999. The deliberate placement of the entire adult female population on Codfish Island (Whenua Hou) in anticipation of an exceptional fruit crop resulted in 95% of them nesting in 2002, raising 24 fledglings and increasing the total population by 39%. Although efforts to increase the frequency of kakapo breeding by providing supplementary food have been unsuccessful, nesting and fledging success increased significantly following the introduction of new, more intensive, management methods in 1995. Hatching success has, however, remained poor, with just 42% of eggs hatching. Comparison with related parrot species suggests that the kakapo’s hatching success is unusually low, perhaps because of inbreeding. Despite infrequent breeding and poor hatching success, the kakapo population has increased by 69% from 51 birds in 1995 to 86 in 2002. The female population has increased from 21 birds in 1995 to 41 in 2002, 20 of which are presently less than 10 years old.