Swift Parrot (Lathamus discolor) is currently listed as Endangered due to a small and declining breeding population and because of the range of threats to the species in both its breeding and wintering ranges.
L. discolor breeds in Tasmania, Australia, mostly along the south-eastern coast from St Helen’s to Southport with a small breeding population in the north near Deloraine. After breeding, birds disperse throughout Tasmania before migrating north to mainland Australia. Both breeding and wintering distributions vary greatly between years, depending on climatic conditions and the resulting food availability (Saunders and Heinsohn 2008). The range in South Australia appears to have contracted, with only irregular recent records of small flocks or individual birds from the south-east of the state. Garnett et al. (2011) estimated a declining population of around 2,000 mature individuals.
L. discolor faces a wide range of threats. Habitat loss and alteration present a major threat, particularly within breeding and drought refuge habitats. When breeding, the species is almost always associated with its main food source, flowering Tasmanian blue gum Eucalyptus globulus, but it has been estimated that flowering may only be sufficient to support breeding in three years out of every 10. Over 50% of the original grassy E. globulus forest in Tasmania has been cleared (Brereton et al. 2004). Competition for remaining nest-sites with Common Starlings Sturnus vulgaris could be a problem along forest edges and competition from large nectarivorous honeyeaters and the introduced bumblebee Bombus terrestris may be exacerbated by forest fragmentation. L. discolor also suffers high mortality through collision with windows, vehicles and fences. Further threats include disease, live capture and the impacts of climate change on habitat phenology.
In 2014 it was reported that L. discolor is also facing a severe threat from the introduced sugar glider Petaurus breviceps in its breeding areas in Tasmania (Stojanovic et al. 2014). Surveys found that the daily survival of nests in areas where sugar gliders occurred was mean 0.97, which equated to a true likelihood of 0.17 for a nest to survive the 60-day nesting period. The threat caused by P. breviceps was greater in locations with less forest cover. Most cases (83.3%) of glider predation also resulted in the death of the adult female parrot. Because the breeding distribution of L. discolor varies widely from year to year, the threat posed by P. breviceps will also vary, depending the occurrence of P. breviceps and the level of forest cover in L. discolor breeding areas. P. breviceps was not detected on Bruny island, which is used as a breeding site by L. discolor.
A study published in 2015 (Heinsohn et al.) used population viability analysis (PVA) to project the future population trend of L. discolor, taking into account the threat of predation by P. breviceps . The model predicted that the population of L. discolor will decline by 78.8%-94.7% (depending on the model used) over three generations (12 – 18 years), with an average predicted loss of 86.9% across all models used. The authors considered these projections conservative, best-case scenarios, partly due to the omission of several likely causes of mortality (including habitat loss) from the models. They suggest that the most appropriate model is that which forecasts a population decline of 94.7% over three generations. The higher survival of L. discolor on offshore islands where P. breviceps is absent was not thought sufficient to buffer the parrot against population decline.
BirdLife Australia’s Threatened Species Committee have recently made the recommendation to its Research and Conservation Committee to uplist L. discolor to Critically Endangered (BirdLife Australia 2015), since the average decline of 86.9% over three generations (16 years) predicted across all models by Heinsohn et al (2015) meets the threshold for Critically Endangered under criterion A3. Unless additional information emerges which suggests that this proposal is invalid, since it is a national endemic we expect that L. discolor will also warrant uplisting to Critically Endangered at the global scale.
Additional information and comments on this proposal are welcomed.
BirdLife Australia. 2015. BirdLife Australia Threatened Species Committee report to RACC. 23rd January 2015. Unpublished report.
Brereton, R. Mallick, S.A. & Kennedy, S.J. 2004. Foraging preferences of Swift Parrots on Tasmanian Blue-gum: tree size, flowering frequency and flowering intensity. Emu 104: 377-383.
Heinsohn, R., Webb, M., Lacy, R., Terauds, A., Alderman, R. & Stojanovic, D. 2015. A severe predator-induced population decline predicted for endangered, migratory swift parrots (Lathamus discolor). Biological Conservation 186: 75-82.
Saunders, D.L. & Heinsohn, R. 2008. Winter habitat use by the endangered, migratory Swift Parrot (Lathamus discolor) in New South Wales. Emu 108(1): 81-89.
Stojanovic, D., Webb, M.H., Alderman, R., Porfirio, L.L. & Heinsohn, R. 2014. Discovery of a novel predator reveals extreme but highly variable mortality for an endangered migratory bird. Diversity and Distributions 20(10): 1200-1207.