Nest protectors provide a cost-effective means of increasing breeding success in Giant Ibis Thaumatibis gigantea

Abstract

SummaryA main cause of nestling loss of the ‘Critically Endangered’ Giant Ibis Thaumatibis gigantea appeared to be mammalian predation. Predator-exclusion devices were added to a randomly selected half of 52 nesting trees, with the other half acting as controls. The number of young fledged per nest was 50% higher for protected nests than control nests. Each protected nest produced almost two-thirds (0.63) of an extra chick. During the nestling period, the daily nestling survival rate was (99.9%) (equivalent to 90% survival over the nestling period) for protected nests and 99.3% (61.3% survival over the whole period) for control nests. Nest protection devices cost US$5 per tree. Each extra nestling fledged as a result of this intervention therefore cost $8. If it was also necessary to pay to locate the nests, then the cost of protecting each nest would be $140 and the cost of producing each extra chick $224. Trees with protectors added were significantly more likely to be reused in the next year than unprotected trees.