Fishers are hard to find. The elusive forest carnivores dwell inside trees and often hunt at night. Unfortunately, spotting this cute cousin of the weasel may become even tougher in western states.

A WCS study has found that the number of fishers in California’s Hoopa Valley Indian Reservation is shrinking quickly. Between 1998 and 2005, the population declined by 73 percent. The researchers suspect a combination of disease, habitat destruction, and less prey is to blame. Increased predation from bobcats might also factor into the fishers’ falling numbers.

Counting these carnivores isn’t easy. Inaccurate methods, the authors say, could lead to misguided land management decisions regarding the species’ future.  For the study, the conservationists scaled tall trees to temporarily capture fishers so that they could attach identification tags to their ears. They then analyzed photographs of the animals taken at remote camera stations, in order to determine how many of them are out there.

“It is critical to understand the status of a population when making decisions about species conservation,” said Sean Matthews, WCS Conservation Biologist. “Our study further demonstrates the importance in monitoring populations of imperiled species and the limitations of some methods in detecting large changes in population size.”

To uncover the threats to fishers and the conservation solutions that can help them recover, the researchers call for more intensive monitoring of the animals and their ecosystems over longer periods of time.

Read more about the study in the press release.