All the eggs in one basket: Are island refuges securing an endangered passerine?

Abstract

Refuges for threatened species are important to prevent species extinction. They provide protection from a range of environmental and biotic stressors, and ideally provide protection against all threatening processes. However, for some species it may not be clear why some areas are refuges and others are not. The fortyspotted pardalote (Pardalotus quadragintus) is an endangered, sedentary, cryptic and specialised bird endemic to the island of Tasmania, Australia. Having undergone an extreme range contraction over the past century the species is now mostly confined to a few small offshore island refuges. Key threatening processes to the species include habitat loss, wildfire, competition and predation. The ways in which these processes have molded the species' contemporary range have not been clearly evaluated. Furthermore, the security of the remnant population within refuges is uncertain. To overcome this uncertainty we assessed key threats and established the population status in known refuges by developing a robust survey protocol within an occupancy modelling framework. We discuss our results in the context of planning trial reintroductions of this endangered species in suitable habitat across its former range. We found very high occupancy rates (0.75-0.96) at two refuges and in suitable conditions, the species was highly detectable (p, 0.43-0.77). At a third location our surveys indicated a local extinction, likely due to recent wildfire. We demonstrate that all refuges are at high risk of one or more threatening processes and the current distribution across island refuges is unlikely to secure the species from extinction. We identified large areas of potential habitat across the species' former mainland range, but these are likely too distant from source populations for natural recolonisation. We propose that establishing new populations of forty-spotted pardalotes via reintroduction is essential to secure the species and that this is best achieved while robust source populations still exist.

Modelling the distribution of a key habitat feature to guide future on‐ground habitat assessment for an endangered specialist songbird

“…Forty‐spotted pardalotes were recently re‐discovered in a small patch of habitat in Southport, on the Tasmanian mainland where the species was last recorded >120 years ago (Webb et al . 2019). Given these small, cryptic birds are less vocal in areas where they occur in low density (probably to avoid aggressive competitors, e.g.…”

“…Although the current distribution of forty-spotted pardalotes is assumed to be known, systematic surveys to look for extant populations beyond known populations have not been conducted. Forty-spotted pardalotes were recently re-discovered in a small patch of habitat in Southport, on the Tasmanian mainland where the species was last recorded >120 years ago (Webb et al 2019). Given these small, cryptic birds are less vocal in areas where they occur in low density (probably to avoid aggressive competitors, e.g.…”

“…2019; Webb et al . 2019). Forty‐spotted pardalotes forage primarily on white gum Eucalyptus viminalis , and local occurrence within their island refuges is governed by the presence of white gums.…”

“…Conservation translocation has been proposed to create insurance populations on the main island of Tasmania (Webb et al . 2019)l, but there is no information on habitat availability and quality to inform planning of reintroduction trials. Because of their restricted contemporary distribution and low number of historical records, SDMs based on sparse pardalote occurrence records may have high uncertainty (i.e.…”

“…The endangered forty-spotted pardalote, Pardalotus quadragintus, is a small songbird endemic to the island state of Tasmania, Australia. Due to ongoing habitat degradation, wildfire, low nesting site availability, competitors and parasites, pardalotes that were once widely distributed in forests where white gums were present across eastern Tasmania now mainly occur on two offshore islands (Bruny and Maria; Appendix S1; Threatened Species Section 2006; Edworthy et al 2019;Webb et al 2019). Forty-spotted pardalotes forage primarily on white gum Eucalyptus viminalis, and local occurrence within their island refuges is governed by the presence of white gums.…”