Non-Invasive Genetic Sampling: A Kinder Approach to Population Estimation

by Ellen Cheng

Almost every wildlife biologist has experienced the sinking feeling of finding an injured or dead animal in a live-trap. Live-traps are used to capture animals, so we can monitor the health of individuals, estimate the number of animals in an area, and collect other information to help us better manage and conserve wildlife populations.

Estimating the size of wild animal populations, however, can be difficult and expensive. While the use of live-traps is the traditional method for calculating such estimates, there is still potential for capture-related injuries and mortalities. Though steps can be taken to reduce such problems, there is little we can do to alleviate the psychological stress of confinement. Some animals when captured will attempt to squeeze or break their way out of live-traps, occasionally injuring themselves in the process. As wildlife biologists, we have a responsibility to actively seek better alternatives for obtaining the data we need.

For the past five years, I’ve been part of a long-term research program studying snowshoe hare abundance estimation, habitat use, and population trends in the western US. The Animal Welfare Institute (AWI) recently funded our program’s study to develop a cost-effective, non-invasive genetic approach to estimate snowshoe hare abundance.

Our study takes advantage of genetic methods that allow us to identify individual animals from the DNA in their hair, scat or other non-invasively collected genetic samples. Though we aren’t the first to use this technique for population estimation, our study is unique in its application to a relatively common species, such as snowshoe hares. Our goal is to increase the general applicability of non-invasive genetic sampling in wildlife research.

Our approach is a simple modification of the basic design used for live-trapping snowshoe hares. A 20-hectare rectangular study site (approximately the size of 48 football fields) is gridded into 80 square plots. In each plot, we lay out a ground cloth baited with apples and alfalfa. While the hares sit and chew on bait, they produce pellets (scat) that contain their unique DNA signatures. The ground cloths are left in the field to “collect” hare pellets for four days. Accumulated pellets on the ground cloths are then brought back to our laboratory, where we apply genetic techniques, among other things, to develop an estimate of hare population size.

So far, we’ve field-tested our approach at two study sites in Glacier National Park, and the results are promising. The population estimates were proximate to those from live-trapping hares at the same sites. Furthermore, our non-invasive approach can be cost-effective (and, in some cases, even cheaper than live-trapping), and is easy to implement in the field.

We’re excited about these results and the promise they hold for broader application. However, our sample size is still too small and our study scope too limited to be conclusive. Therefore, we will be applying our approach at additional study sites this summer on commercial forest lands.

Ellen Cheng is a PhD candidate in the University of Montana’s Wildlife Biology program. She has more than a decade of experience managing and implementing field research projects on a variety of taxa, from birds and reptiles to small mammals and ungulates. Prior to returning to graduate school, she served four years as Director of Development for The Natural Heritage Institute, a conservation nonprofit organization in Berkeley, Calif.