How do we count rare wildlife?

Photo credit: US FWS/Joe Milmoe

A recent study suggests that one of the most popular ways that scientists estimate populations of rare, threatened or endangered wildlife can be inaccurate, which is bad news for managers, conservationists, and wildlife.

Field science can be expensive, time consuming, and require a lot of man (and woman!) power. So instead of trying to count every individual sloth, or tiger, or salamander, scientists often rely on something called index-calibration. This process involves counting a target species as accurately as possible in a small area, using expensive and intense techniques like motion-activated camera traps. This accurate count is then correlated to simpler, less expensive methods like counting tracks. The rougher estimate from the area that has been measured as accurately as possible is used to “calibrate” the counts in other areas based solely on less expensive (and less accurate) measures.

It’s easy to think that good field science will always yield good results, but the ways that data are interpreted and analyzed can be just as important. Statistical ecologists found that when there was even 10 percent uncertainty about the detection rates of wildlife in the more accurate measure, index-calibration loses the ability to accurately predict wildlife numbers. This technique was used recently in a study which found a thirty percent increase in tiger numbers in India in just eight years (which was great news, but pretty surprising!). When the mathematicians experimented with the field data themselves, they found that even small inaccuracies in detection rates could lead to dramatically different results from the model. While it’s sometimes true that field scientists and the mathematically-inclined scientists who build and test these models don’t fully appreciate each other’s contributions, this finding is an important reminder that good science doesn’t end in the field—good field notes, data, and sample labeling is only the beginning of a long and complex scientific process! 

If you're curious (and mathematically inclined yourself!) the paper reference is:
 Gopalaswamy AM, Delampady, KM, Ullas Karanth, N, Kumar S,  Macdonald, DW. An examination of index-calibration experiments: counting tigers at macroecological scales. Methods in Ecology and Evolution, 2015; DOI: 10.1111/2041-210X.12351.