The conservation of animals relies heavily on estimates of their numbers. Without knowing how many individuals there are, it is impossible to know whether a population is thriving or dying out—and whether conservation efforts are getting the job done. But making those estimates is no mean feat, reports Easton R. White of the Center for Population Biology at the University of California, Davis, writing in BioScience. Unfortunately, he says, many monitoring periods of threatened species are short, a result of “short funding cycles and typical experimental time frames.”