Polar bears, like other large predators, are hard to track and count, and available data is often fragmentary and difficult to piece together. Now, a new model provides estimates for key parameters for polar bears in the Chukchi Sea off north-western Alaska, by combining available data from telemetry, marking and recapturing, and counts. The model estimates that 83% of females give birth every year, that litter sizes are 2.11 per year, and that survival is about 90% for both males and females. Densities of polar bears in this region appear little changed from surveys in the 1980s, and suggest that this population contains nearly 3,000 polar bears (although the numbers could be anywhere from 1,600 to 5,900). The new research was led by Eric Regehr of the US Fish and Wildlife Service, included SAFS professor Sarah Converse among the coauthors, and was published in the journal Scientific Reports.