Testing the decline of the threatened New Holland Mouse (Pseudomys novaehollandiae)

Abstract

Delineating the distribution of a threatened species is critical for identifying threats and guiding conservation management. The process is challenging, however, especially when a species is rapidly declining, and so changing its distribution. In this context, species distribution modelling (SDM) often lacks the precision needed to inform fine-scale management decisions, but on-ground surveys to test species’ distributions are time and resource intensive. The dilemma can be mitigated to some extent by careful examination of historical data, and optimal monitoring.

The New Holland Mouse (NHM; Pseudomys novaehollandiae) is one of many Australian rodent species to have undergone drastic distributional declines since European invasion. Initially recorded in Victoria in 1970, by 2015 NHMs were thought to occur in only 3 of 12 historically occupied regions. I tested this decline with statistical rigour, using extensive Elliott and camera trapping surveys at >500 sites across Victoria. Combining my survey data with 48 years of others’ efforts, I evaluated the utility of standard Elliott trapping surveys and the efficacy of camera trapping for NHMs. I tested whether NHMs were where we would expect based on state-government threatened fauna SDMs, and whether the species’ purported early-successional fire association explained occurrence or abundance.

I confirmed the species’ persistence in 5 of 12 historical regions – including regions where NHMs had not been detected in 5-21 years – and expanded the species’ known distribution in two regions. However, these finds can be attributed to a paucity of prior survey effort and were partnered with greater declines elsewhere. Elliott trapping surveys were often inadequate to provide statistical confidence in the species’ absence; camera trap surveys provide a viable alternative for distribution assessments. Standard state-government SDMs provided limited guidance as to the true distribution of NHMs and SDMs for declining species should be interpreted with caution. Time-since-fire did not explain the species’ occurrence and poorly explains abundance, though in certain locations inappropriate fire regimes are a threatening process. Predator control, habitat management, and careful reintroductions are key priorities for conservation of NHMs in Victoria.