Back to the brink: Population decline of the endangered Grassland Earless Dragon (Tympanocryptis pinguicolla) following its rediscovery

Abstract

Lizard populations are under serious threat through widespread decline and predictions of multiple extinctions through climate change. Yet detecting specific instances of decline remains problematic in many situations because of inconsistent and sparse data. We assessed the stability of populations of the endangered Grassland Earless Dragons (Tympanocryptis pinguicolla) conducted after its rediscovery using capture rates at 10 sites (from 23 surveyed) and survival and population size estimation at one intensively studied site. We show a gradual non-significant decline in population size across all sites from 1995 followed by a dramatic reduction (88%) from 2006 at the most densely populated site. Using mark-recapture-release approaches, we estimate annual survival at that site to be low (0.017 to one year of age and 0.024 to adulthood) over the three years of the study. Taken together, these data suggest a regional decline among T. pinguicolla populations that place the species in grave jeopardy of becoming the first confirmed reptile extinction in Australia since European settlement. The key factors for basing further hypothesis driven monitoring include drought habitat cover (or the effects of grazing) and habitat fragmentation. We agree with other conservationists that for highly endangered species, there may not be the time required to conduct long-term monitoring. However, by making good use of even disparate past surveys, a case can be made for trends in population size. We urge that even data collected in an ad hoc manner be examined to help plan management programs for rare or endangered species.