The impact of predation on the kereru (Hemiphaga novaeseelandiae) on Banks Peninsula

Abstract

The kereru (New Zealand Pigeon, Hemiphaga novaeseelandiae) is a threatened endemic species. Predation of eggs, chicks, and adults at nests by mammalian predators is considered to be a major potential threat. The impact of mammalian predators on kereru populations was studied on three remnant native bush areas on Banks Peninsula, New Zealand, from February 2004 to March 2005.

Artificial nests were used to monitor predator activity and to identify potential predators to kereru nests. Artificial nests consisted of a wicker basket, a wax egg and a hen egg. Rats were identified as a significant predator of nests (70% of total nest predation). Other predators identified by the artificial nests were possums (20%), mice (7%), stoats (0.4%) and unknown (2%). It is suggested that artificial nest studies should not replace studies of real nests. Rather, they are a useful supplement to data on real nests.

Kereru display flights were monitored to determine the onset of breeding. Display flights were observed from July to September 2004. Display flight frequency, the proportion of total flights observed that were display flights, was highest at 22% of total flights in July. The frequency of display flights decreased to 15% of total flights in August as one pair had begun to nest. By September pairs were nesting in Church Bay and not performing display flights.

Kereru nests were located by following 15 kereru fitted with radio-transmitters. Nests were intensely monitored for signs of predation by video monitoring and direct observation. A total of 20 nests were located, of which 11 failed, seven the result of predation. Seven chicks fledged giving a nesting success rate of 35%. Rats and possums were identified as predators of two eggs and implicated in the loss of another five eggs. A cat preyed on a nestling chick and also ate the brooding female.

Three radio-tagged kereru were lost at the beginning of this study and their transmitters were redeployed. So 18 radio-tagged kereru were monitored for predator-induced mortality. Five adult kereru died, three as a result of predation. A cat was recorded on video preying on one adult. It is hypothesised that cats were responsible for preying on other kereru during this study.

Rat and possum predation limited nesting success however, this could have been offset by replacement nesting after nest failures. Cats preyed on chicks and adult kereru which impacted on the breeding viability of the adult population. Kereru may be able to withstand some nest predation pressure if the pair are able to re-nest in the same season. However, the ability of kereru to re-nest is reliant on them having an adequate food source, so this may not be possible in poor seasons.

These assertions of when predator control is most needed would benefit from population modelling to determine their relative importance. Nesting success would benefit from rat and possum control during good breeding seasons. Adult survival would benefit from the control of predators such as cats and stoats. However, as kereru have integrated into urban habitat, managers must consult with the community before conducting predator control.