Search

Dimensions of body size are an important measurement in animal ecology, although they can be difficult to obtain due to the effort and cost associated with the invasive nature of these measurements. We avoid these limitations by using camera trap images to derive dimensions of animal size. To obtain measurements of object dimensions using this method, the size of the object in pixels, the focal length of the camera, and the distance to that object must be known. We describe a novel approach of obtaining the distance to the object through the creation of a portable distance marker, which, when photographed, creates a "reference image" to determine the position of the animal within an image. This method allows for the retrospective analysis of existing datasets and eliminates the need for permanent in‐field distance markers. We tested the accuracy of this methodology under controlled conditions with objects of known size resembling Felis catus, our study species, validating the legitimacy of our method of size estimation. We then apply our method to measure feral cat body size using images collected in Tasmania, Australia. The precision of our methodology was evaluated by comparing size estimates across individual cats, revealing consistent and reliable results. The average height (front paw to shoulder) of the feral cats sampled was 25.25 cm (CI = 24.4, 26.1) and the average length (base of tail to nose) was 47.48 cm (CI = 46.0, 48.9), suggesting wild feral cats in our study area are no larger than their domestic counterparts. Given the success of its application within our study, we call for further trails with this method across a variety of species. [ABSTRACT FROM AUTHOR]

The Thylacine or 'Tasmanian tiger' (Thylacinus cynocephalus), an iconic canid-like marsupial predator and last member of its taxonomic family (Thylacinidae) to have survived to modern times, was declared officially extinct in the early 1980s, half a century after the death of the last captive animal. However, the regularity and frequency of sightings of the species over more than eight decades since has not only created a zoological mystery, but also made it challenging to reconstruct the timeline of the fate of the species. To help resolve this intriguing historical-ecological problem, we compiled and curated a comprehensive inventory of documented sighting records from Tasmania from 1910 to 2019. By examining sources spanning official archives, published reports, museum collections, newspaper articles, microfilm, contemporary correspondence, private collections and other miscellaneous citations and testimony, we have amassed 1,223 unique Thylacine records from this period and resolved previous anomalies and duplications. Each observation in the database is dated, geo-tagged, categorised, quality-rated, referenced and linked to an image of its source material. Although purported observations have occurred every year, reporting rates vary across the decades in terms of frequency, type, location, and quality rating. Here we describe the database in detail, highlight its value for research, interpret the major patterns revealed by this archival compilation, and discuss the broader implications of the result of this work on the likely time and place of the Thylacine's extinction in the wild. [ABSTRACT FROM AUTHOR]

Avoiding the undesirable impacts of invasive species requires robustly evaluating the effects of alternative management scenarios. Such evaluations depend on reliable spatio‐temporal projections of changes in the distribution and abundance of the invasive species under different scenarios. However, commonly used modelling approaches are constrained for this purpose because they do not incorporate demographic processes and are seldom validated.We develop a spatially and temporally explicit grid‐based population model for invasive fallow deer Dama dama in Tasmania, Australia, validated against observed distribution and abundance 'targets' using a pattern‐oriented approach. We use this validated model to project the future invasion patterns of deer, including encroachment into areas of high conservation value, under eight harvest and habitat suitability scenarios.Projected population sizes of deer differ greatly depending on harvest and habitat suitability scenarios. Without harvest, the population grows sixfold, from about 80,000 deer in 2019 to over 500,000 by 2100. In contrast, the population stabilises at 32,000–41,000 deer with 25% annual harvest. Abundance in the environmentally sensitive Tasmanian Wilderness World Heritage Area (TWWHA), a region of high conservation value, increases in all scenarios. We identify likely areas in the expanding range of deer where targeted removal should be most effective at minimising deer numbers in the TWWHA.Synthesis and applications: Using a pattern‐oriented model validated with spatio‐temporal data, we show how the future distribution and abundance of invasive fallow deer in Tasmania can be substantially reduced by targeted increases in harvest and prioritising areas for removal around high conservation value regions. Our approach can be used to project likely effects of management interventions on future distributions and abundances for a range of invasive taxa. [ABSTRACT FROM AUTHOR]