Conservation in the context of prevailing data deficiency: the case of the Tasmanian masked owl.

Abstract

Rarity, elusiveness, ineffective methods and limited resources inhibit conservation research. Data-deficiency conceals threats and priorities, prolonging indecision in conservation. Tackling data-deficiency needs integrated research approaches. Meanwhile, understanding the impact of data-deficiency in conservation scenarios can guide research and allow confident evaluation of new information by management. I studied the Endangered Tasmanian masked owl (Tyto novaehollandiae castanops), a secretive forest bird, and a model data-deficient species. The species is difficult to observe, and sparse data means available knowledge is inferred from small samples, expert opinion or anecdotes. I used a generalised framework integrating methods that use field data and others that use existing data resources, to address limitations in knowledge arising from data-deficiency and assess the potential impacts of data-deficiency in threat assessment. This approach potentially avoided paralysis arising from limitations encountered in any given approach. Four studies targeted knowledge gaps and a fifth study demonstrated the use of quantitative models to evaluate the impact of data-deficiency in assessments of threat scenarios. Forestry threatens masked owls but owl occurrence in forests is rarely surveyed. My first study estimated occupancy in a landscape shaped by logging. Prey abundance influenced occupancy, but detection rates were low, using call-broadcast, and models with high predictive power were not achieved. Traces (e.g. scats) can improve detection of elusive species, and associated DNA can be used to estimate abundance. I developed genotypes from trace DNA (feathers/pellets) as genetic tags for owls. Poor DNA quality could limit some applications of traces; however, this study increased opportunities for studying owl ecology. The masked owl population is expected to decline. My third study assessed population genetic structure and diversity, using museum specimens. The results show a single genetic conservation unit shaped by isolation by distance, and an effective population size in decline. This result validates concerns for the trajectory of the population. Masked owl vulnerability to climate change is unknown. My fourth study investigated the roles of climate and prey occurrence on masked owl distribution. The masked owl is resilient to some future changes in the Tasmanian climate, however, the effects of climate change on prey distributions may limit where the owl persists in drier and hotter climates. Uncertainty will remain despite our best efforts. My fifth study assessed the effect of uncertainty in an emerging threat scenario, rodenticide exposure, using population viability analysis. The effect of rodenticides on population growth was negative, however, the magnitude depended on the baseline juvenile mortality rate used in each model, highlighting the importance of obtaining more accurate estimates of this uncertain parameter. My thesis demonstrated how integrated research can broadly target prevailing data-deficiency. Trace DNA increased opportunities to estimate population parameters. Meanwhile, I used genetics to update population estimates and validate the species' endangered status. I revealed a potential vulnerability of owls to climate change. Finally, I demonstrated the potentially major negative impact of rodenticides on masked owl population growth rates, despite data uncertainty concealing this threat. Integrated research can help guide recovery plans by reducing data-deficiency and increasing understanding of the impact of residual data-deficiency for conservation. Show more