Tracking animal movements using biomarkers in tail hairs: a novel approach for animal geolocating from sulfur isoscapes

BACKGROUND

Current animal tracking studies are most often based on the application of external geolocators such as GPS and radio transmitters. While these technologies provide detailed movement data, they are costly to acquire and maintain, which often restricts sample sizes. Furthermore, deploying external geolocators requires physically capturing and recapturing of animals, which poses an additional welfare concern. Natural biomarkers provide an alternative, non-invasive approach for addressing a range of geolocation questions and can, because of relatively low cost, be collected from many individuals thereby broadening the scope for population-wide inference.

METHODS

We developed a low-cost, minimally invasive method for distinguishing between local versus non-local movements of cattle using sulfur isotope ratios (δ34S) in cattle tail hair collected in the Greater Serengeti Ecosystem, Tanzania.

RESULTS

We used a Generalized Additive Model to generate a predicted δ34S isoscape across the study area. This isoscape was constructed using spatial smoothers and underpinned by the positive relationship between δ34S values and lithology. We then established a strong relationship between δ34S from recent sections of cattle tail hair and the δ34S from grasses sampled in the immediate vicinity of an individual's location, suggesting δ34S in the hair reflects the δ34S in the environment. By combining uncertainty in estimation of the isoscape, with predictions of tail hair δ34S given an animal's position in the isoscape we estimated the anisotropic distribution of travel distances across the Serengeti ecosystem sufficient to detect movement using sulfur stable isotopes.

CONCLUSIONS

While the focus of our study was on cattle, this approach can be modified to understand movements in other mobile organisms where the sulfur isoscape is sufficiently heterogeneous relative to the spatial scale of animal movements and where tracking with traditional methods is difficult.

Management of Himalayan thar (Hemitragus jemlahicus) in New Zealand: the influence of Graeme Caughley

Graeme Caughley developed many of his ideas on wildlife management, and how it should be underpinned by evidence rather than by dogma, during the mid-1960s when he was working for the New Zealand Forest Service and doing the fieldwork for his Ph.D. on the population dynamics of Himalayan thar in the Southern Alps of New Zealand. However, there was a 30-year lag between the advice on the management of wild animals Caughley was providing to the New Zealand Government in the 1960s and its uptake in a national plan to manage thar in the 1990s. Eventually his ideas of setting measurable goals that were based on science, in this case on his ideas on interactive systems between herbivores and their food supply, and on management systems that led to stable outcomes were at least partially taken up. This paper reviews how some of Caughley’s ideas were, or were not, included in a plan developed in 1993 and its subsequent application to manage Himalayan thar in New Zealand.