Utilization of modified and artificial nests by endemic and introduced parrots on Norfolk Island

Animals that breed in cavities formed through decay or mechanical damage often face limitations to reproduction due to a shortage of nest sites. Artificial nests are commonly deployed to increase the short-term availability of breeding sites for these species. Often this is an effective approach; however, artificial nests are costly and may be ignored by the target species or inadvertently benefit nontarget species. Here we consider the use of modified natural hollows and artificial nest sites to support endangered Norfolk Island green parrots Cyanoramphus cookii. We recorded the characteristics of all modified and artificial nests in the Norfolk Island National Park and used 8 years of nesting data to study nest selection by green parrots and introduced crimson rosellas Platycercus elegans. Artificial nests (those lacking a natural base) were never used by green parrots. Nests with thicker walls were more likely to be used by green parrots, but there was no nest site characteristic that predicted frequency of use. Crimson rosella nest use was not predicted by any of the nest characteristics measured. A better understanding of the reasons behind green parrots' avoidance of artificial nests and preference for thicker nest walls is required to inform the future design and management of nest sites. Our study shows that evaluation of how artificial sites are used by the target species is important to maximize the efficacy of conservation efforts.