Nest predator abundance and its relationship with regent honeyeater (Anthochaera phrygia) nest success

Abstract

Woodland bird populations continue to decline in south-eastern Australia. As a result of habitat loss and fragmentation woodland birds now face novel threats, including elevated rates of nest predation. Nest predation presents a damaging selective pressure for threatened species, preventing recruitment to, and recovery of, small populations. It is the leading cause of nest failure for the critically endangered regent honeyeater (Anthochaera phrygia), which has already experienced rapid population decline. A number of common avian and mammalian species have been observed depredating regent honeyeater nests in recent studies. I surveyed diurnal and nocturnal nest predators in key regent honeyeater breeding areas to develop an understanding of the distribution and predictors of nest predators and to examine the impact of predator abundance and species richness on regent honeyeater nest success. I surveyed 12 species of nest predators at 246 study sites between August and November 2019. I used repeat point-count surveys for diurnal and nocturnal predators, and conducted scat surveys as an additional indicator of common brushtail possum (Trichosurus vulpecula) presence. Results showed that predator abundance and predator species richness were significantly higher at sites near water, with high hollow abundance and where short grass was the dominant ground cover. Predator species richness was also higher at sites with moderate (15 – 30%) canopy cover. Both predator abundance and species richness were slightly elevated at regent honeyeater nest sites, although these results were non-significant. I used data from 115 regent honeyeater nests from the last five years to examine the impact of predator abundance and predator species richness on nest survival. Predator abundance and predator species richness were positively related to nest success, indicating that high levels of predator abundance were not associated with regent honeyeater nest failures. While unexpected, these results suggest that other factors may be causing variation in nest predation rates, including regent honeyeater anti-predator strategies, resource availability and / or differing rates of learned predatory behaviour across sites. Despite a positive correlation between regent honeyeater nest survival and nest predators, nest success was low (31.6%). Further research is required to identify the most significant drivers of nest predation rates, in order to better understand variances in regent honeyeater nest success and inform effective manage of the species.