Discovery of a novel predator reveals extreme but highly variable mortality for an endangered migratory bird

Abstract

Aim Introduced predators are a global driver of species decline, but their impact on highly mobile species is poorly understood. We report the severe impact of a previously undocumented introduced predator on the endangered, migratory swift parrot (Lathamus discolor). Sugar gliders (Petaurus breviceps), a supposedly benign introduced species, were detected acting as a major opportunistic predator of cavity-nesting birds. We assessed the intensity and geographical extent of sugar glider predation and investigated whether habitat loss exacerbated predation risk to swift parrots.Location Tasmania, Australia.Methods We monitored nests of swift parrots for 3 years with motion-activated cameras. We used bioclimatic modelling to predict the potential distribution of introduced sugar gliders across the study area and assessed the predation risk to swift parrots and other threatened birds in the region using nest-survival analysis.Results 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. No nests failed on an offshore island where sugar gliders were shown to be absent. Most cases (83.3%) of glider predation resulted in the death of the adult female parrot. On the Tasmanian mainland, there was a positive relationship between nest survival and increasing mature forest cover at the landscape scale.Main conclusions Predation risk varied dramatically across the breeding range of swift parrots, depending on the presence of sugar gliders. Offshore islands are an important refuge for swift parrots because sugar gliders are absent. However, islands are vulnerable, and our bioclimatic model shows that they are bioclimatically suitable for sugar gliders. Synergistic interactions between predation and habitat loss combine with low breeding-site philopatry to expose swift parrots to dramatic variation in predation risk depending on nesting location.

Resource requirements of parrots: nest site selectivity and dietary plasticity of Psittaciformes

“…In another study, number of fledglings produced by the Eclectus Parrot (Eclectus roratus) was significantly related to the depth and dryness of the nest cavity (Heinsohn 2008). Other studies have determined that factors such as forest canopy cover or proximity to waterways significantly influence nest success and productivity as these features may facilitate predator access to nests or be associated with anthropogenic activities (Bonebrake and Beissinger 2010;Britt et al 2014;Stojanovic et al 2014). In their study on 27 cavity-nesting bird species, including two small-bodied parrot species and three larger parrot species, Cockle et al (2015) observed that the nest success of the smaller cavity-nesting species was predicted by cavity height and entrance diameter, while tree condition was an important variable for nest success of larger species.…”

Acoustic differences enable sex discrimination in Ma'oma'o (Gymnomyza samoensis), a species with high sexual morphological overlap

“…In species where vocalizations are sexually dimorphic, such as the Ma'oma'o, using recordings and automatic techniques to recognize vocalizations may be useful for the future assessment of sex ratios. Employing such a method may be particularly useful for monitoring species where higher population declines are occurring in a single sex, such as Kaka (Greene andFraser 1998, Wilson et al 1998), Seychelles Magpie Robin (Copsychus sechellarum; Gerlach and Le Maitre 2001) and Swift Parrot (Stojanovic et al 2014). Understanding sex ratio differences may also be important in aiding conservation of the Ma'oma'o.…”

“…However, as it can be used on DNA from a molted feather, it is not always necessary to capture the bird. Techniques that overcome these restrictions are needed for robust management and conservation, particularly for declining species [e.g., Kaka (Nestor meridionalis; Wilson et al 1998); and Swift Parrot (Lathamus discolor; Stojanovic et al 2014)]. A quick, simple, field-based test of sex is particularly vital where a greater decline in one sex is suspected or knowledge of the sex ratio present in a population is needed for wildlife management (Martin 1996, Winkler and Preleuthner 2001, Wolfe et al 2010.…”

“…For example, in Swift Parrots and Kaka, only the female incubates and as a result experiences higher mortality on the nest from predators. Unequal predation across the sexes results in unequal sex ratios, which may contribute to the decline of the species (Wilson et al 1998, Moore et al 2010, Stojanovic et al 2014.…”

Settlement and Swift Parrots — historic and ongoing habitat loss for a critically endangered species (1788–2016)

“…10). For example, Stojanovic et al (2014) clearly demonstrate the extreme cumulative impact on the Swift Parrot from forest management practices that reduce the amount of mature habitat available.…”