Growth and survival of nestlings in a population of red-crowned parakeets (Cyanoramphus novaezelandiae) free of introduced mammalian nest predators on Tiritiri Matangi Island, New Zealand
- Ecology and Conservation Lab, Institute of Natural and Mathematical Sciences, Massey University, Private Bag 102-904, North Shore Mail Centre, Auckland, New Zealand
- Charles Darwin Foundation, Puerto Ayora, Galapagos Islands, Ecuador
- Department of Psychology, Hunter College and the Graduate Center of the City University of New York, NY 10065, USA
The negative effects of introduced nest predators on the breeding success of endemic New Zealand parrots are well documented, as is their role in the general decline of these species. In contrast, little is known about the intrinsic intra-brood dynamics responsible for modulating fledging success in parrots breeding at sites free of introduced nest predators. We studied red-crowned parakeets over two breeding seasons on Tiritiri Matangi, an offshore island free of introduced mammalian predators. We analysed the patterns of hatching and survival, and the sex-specific growth of nestlings in relation to clutch initiation date and natural levels of hatching asynchrony. We also explored the relationships of nestling sex and hatching rank on survival. Earlier laid clutches resulted in larger broods which in turn produced more nestlings in better body condition, independent of the sex of the nestlings. Similar to many other bird species with extensive hatching asynchrony, last hatched red-crowned parakeets suffered higher mortality than other hatch ranks. Primary sex ratios and sex ratios at hatching and fledging did not deviate significantly from parity. Our results indicate that in the absence of nest predation by exotic predators, the timing of clutch initiation and brood reduction due to starvation of last hatched nestlings are the most important determinants of nestling survival and growth in red-crowned parakeets. Consequently, from a conservation management perspective, the close monitoring of target populations during the breeding season is recommended to estimate nestling survival and nest productivity when planning the timing of capture of wild birds for translocations or harvesting potential breeding stock for captive breeding programmes.