Documenting demise? Sixteen years observing the Swift Parrot Lathamus discolor in suburban Hobart, Tasmania

Abstract

The Swift Parrot Lathamus discolor is listed as Critically Endangered because modelling suggests that its population is declining by > 80% within three generations (12-18 years) as a result of just one of many factors impacting the species: predation by introduced Sugar Gliders Petaurus breviceps. Unfortunately, verification of this prediction through monitoring of the entire population across its breeding range is difficult because of the amount of observer effort required to count all individuals within the often dense canopies of Eucalyptus trees, where it forages predominantly from flowers. This study entails 16 years of opportunistic observations at a single location within this species’ breeding range. Regression models indicated that over 16 breeding seasons the mean size of the largest flock per month declined by ∼90%, and grand mean size of all flocks per month by ∼70%. This was not the result of decreasing local flowering intensity in the Swift Parrot’s favoured food plants, as adjusting the two measures of abundance for local inter-annual variation in flowering had little effect on the rates of decline. This concordance between observations at the local scale and modelling of the entire population supports the findings of the modelling, suggesting that urgent action is required to prevent extinction of this species.