Estimating wildlife population trends: the case of the Helmeted Honeyeater

Abstract

Assessing trends in wildlife populations involves estimating whether those populations are stable, increasing or decreasing, and trends can infer the success or failure of management. This paper determines trends in a population of critically endangered Helmeted Honeyeaters (Lichenostomus melanops cassidix) in Victoria, Australia, using a range of estimation procedures. Analyses of breeding pairs data show the population of Helmeted Honeyeaters increased, with an annual finite growth rate (λ) of 1.07 (95% confidence intervals 1.02-1.12), over 8 years (1989–90 to 1996–97) then decreased over 12 years (1997–98 to 2008–09) with λ of 0.94 (95% CI 0.91-0.96). Demographic analysis estimated that during the first 8 years λ was 1.21 (95% CI 1.01-1.40), which overlapped the estimate of λ from breeding pairs data but was less precise. There were no demographic data for the later period of 12 years. The number of breeding pairs in 1 year was positively, although only weakly (R2 = 0.23), and significantly (P = 0.03) related to annual rainfall 2 years prior. Wildlife management, such as that of Helmeted Honeyeaters, needs ongoing, quantitative assessment of trends involving measures such as λ, with associated 95% CI.