Overfeeding Kakapo creates a bias in the sexes.

25/12/2006 00:00:00 Supplementary feeding is often a key tool in the intensive management of captive and threatened species. Although it can increase such parameters as breeding frequency and individual survival, supplementary feeding may produce undesirable side effects that increase overall extinction risk.

Recent attempts to increase breeding frequency and success in the kakapo using supplementary feeding inadvertently resulted in highly male-biased chick sex ratios.

The kakapo is a critically endangered New Zealand parrot that has been subject to supplementary feeding since 1989: feeding improves female condition and egg and chick survival. Although supplementary feeding has been adaptively managed to avoid short-term negative effects, such as female obesity, little consideration was given to long-term effects until it was suggested that increased maternal condition associated with supplementary feeding might influence sex ratios in kakapo.

As predicted from evolutionary theory and kakapo life-history traits, such as lek mating skewed male reproductive success based on body size and larger faster growing male nestlings than females, analysis of sex allocation in kakapo revealed that fed females produced more sons than daughters, 70% of offspring were male.

Male-biased production in an already male-biased population (currently 45 males:38 females) represents a critical challenge to kakapo recovery by prolonging species recovery and the risk of extinction. The solution to this dilemma, though, is not simply to cease supplementary feeding, because feeding plays a significant role in kakapo recovery.

Female kakapo do not breed unless they are above a threshold weight of 1.5kg hence supplementary feeding can ensure all females are above the threshold weight prior to the breeding season and hence, potentially stimulate breeding.

Bruce C. Robertson, Graeme P. Elliott, Daryl K. Eason, Mick N. Clout, Neil J. Gemmell.

University of Canterbury School of Biological Sciences PB 4800, Christchurch, New Zealand

Kakapo Management Group Department of Conservation PB 5, Nelson, New Zealand

University of Auckland Centre for Biodiversity and Biosecurity PB 92019, Auckland, New Zealand

The full research can be seen in the Royal Society Biology Letters.
ISSN: 1744-9561 (Paper) 1744-957X (Online)
Issue: Volume 2, Number 2 / June 22, 2006