Influence of extreme and typical rainfall on nestling body condition of the endangered Norfolk Island Morepork: conservation implications of climate change

ABSTRACT

Species on small, isolated islands are particularly prone to extinction from human-related threats including climate change. As a case study, we investigated body condition of nestlings of the critically endangered, conservation-dependent subspecies of Tasman Moreporks Ninox novaeseelandiae on Norfolk Island. Annual productivity is low, with only 53 fledglings produced on the island 1989–2007, two in 2019 and an unknown number between. As predicted under climate change, the island is experiencing increasingly drier conditions and more extreme precipitation events. It was postulated that this would negatively impact on body condition. A condition index for 48 nestlings was positively correlated with typical annual rainfall (<1500 mm), but depressed in years of extreme precipitation (>1871 mm). Optimal nestling condition coincided with long-term, median annual rainfall and female nestlings were in better condition than males. The timing of breeding became progressively later over the study period. These results are interpreted as food resource-related, via prey availability and hunting conditions. Implications include that in dry years and under very wet conditions, some adult females may be unable to put on sufficient weight to attempt to reproduce and those that do breed may produce fewer nestlings, and, importantly, that the current population may be around capacity. Conservation efforts should take into consideration the impacts of climate change, particularly on small, human-impacted islands, where species face interacting threats, and resources and options for adaptation are severely limited.

KEYWORDS:

• Endangered owl
• body condition
• climate change
• productivity
• breeding season
• islands

Acknowledgements

We are grateful to the Norfolk Island Parks Australia team, and their earlier equivalents, especially Derek Greenwood and Ron Ward, without whose diligence and skill in the field this paper would not have been possible, and for the support of several conservators, who funded travel for PO to and from the island over many years. Mike Double conducted the PCR tests to sex several nestlings. Thanks also to Mel Wilson for nestling data from the 2019 season. Comments from Denis Saunders, Victoria (Flossy) Sperring, three anonymous referees and the editor greatly improved the paper.

Disclosure statement

No potential conflict of interest was reported by the author(s).