Recruitment, survival and breeding success in a declining rifleman population

We used detailed life-history data collected over a six-year period from a colour-banded population of riflemen (Acanthisitta chloris) at Kowhai Bush, near Kaikoura, to estimate population vital rates and assess their likely contribution to a concurrent population decline. Both mean juvenile survival (18%) and mean adult survival (49%) were low in comparison with reports from other populations. In contrast, breeding success was high, with pairs producing c. 3 fledglings per season on average. High breeding success was likely associated with nestbox use. We then used survival and breeding success estimates to parameterise a population matrix model, and perturbation analysis of this model confirmed a projected negative trend, with reduced recruitment having the greatest absolute contribution to population decline. We discuss possible explanations for the comparatively low rates of recruitment and survival observed. Data from other populations of riflemen experiencing stable or positive population trajectories would be especially useful to better understand factors affecting vital rates, and to identify the thresholds that signal a rifleman population at risk of decline.

Automated summary

We used six years of detailed life-history data from a population of riflemen to estimate vital rates and understand their contribution to the population decline. Juvenile and adult survival rates were low compared to other populations, while breeding success was high. A population matrix model confirmed a negative trend, with reduced recruitment being the main factor contributing to the decline. More data from populations with stable or positive trends would be helpful for understanding the factors affecting vital rates.