Counting Svalbard reindeer

Submitted by editor on 21 November 2017.

What's the best way for counting reindeers? Mathilde Le Moullec and colleagues have sorted it out in the paper "Ungulate population monitoring in an open tundra landscape: distance sampling versus total counts". Read their summary here:

Counting reindeer on the open tundra is more complex than counting the number of legs and dividing by four! We may miss some reindeer or even count others twice. Although often fundamental for scientific studies as well as management decisions, the uncertainties associated with animal abundance counts are rarely investigated, regardless of the counting method used. Wild Svalbard reindeer, which occur alone or in very small groups, have been censused for several decades by total population counts in small isolated areas, such as the peninsulas close to the Ny-Ålesund scientific base. However, such total counts are not possible in large and less clearly defined areas. Therefore, we explored the pros and cons of different survey methods by comparing abundance estimates from repeated total counts with the commonly used methodology of distance sampling along transect lines. Distance sampling, which takes into account the distance from the detected animal to the transect line (see picture) and landscape covariates affecting detection and/or density, has rarely been evaluated in wild populations with “known” population size. As expected in these small open tundra peninsulas, total counts turned out to be highly precise and unbiased while distance sampling abundance estimates were considerably less precise. We conclude that distance sampling can be a cost-effective tool suitable for large-scale density estimates and population state assessments. However, capturing the mechanisms driving the population dynamics from year to year likely requires high sampling effort or other, more resource demanding monitoring methods, such as total counts or mark-recapture. In the case of wild Svalbard reindeer, which were almost eradicated a century ago but then have recolonized most of the archipelago, no reliable estimates are available on total abundance. Based on the lessons learned from this study – applying distance sampling or total count according to site-specific characteristics – and an extensive survey across the entire archipelago, we are now estimating the distribution and abundance of the entire sub-species. Hopefully, once multiplied by four, this will give an idea of the numbers of legs!