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Denning Phenology, Den Substrate, and Reproductive Success of Female Polar Bears (Ursus maritimus) in the southern Beaufort Sea 1986-2013 and the Chukchi Sea 1987-1994

July 21, 2021

These data represent estimates of den entrance and exit dates for female polar bears in the southern Beaufort and Chukchi Seas based on temperature sensor data obtained from satellite collars. An algorithm described in Olson et al. (2017) was used to determine whether the female entered a den and further analyses using temperature data as described in Olson et al. (2017) were used to assess den entry and emergence dates. The algorithm used identified the denning period as that during which collar temperature remained consistently above a temperature threshold. As such, users of these data should be aware that bear behavior can affect den entrance and exit date. If a bear moves in and out of a den frequently, the algorithm identifies that bear as not denning. Den substrate was determined by examining satellite locations from collars during the identified denning period and classify dens as occurring on landfast ice, pack ice, or land. This data set also includes direct observations of females post-den emergence to ascertain whether or not she was accompanied by cubs as an indicator of reproductive success. The den IDs provided in this data set correspond with those identified in the USGS den catalog (Durner 2010, Durner et al 2020) additional information about the dens in this data set may be found in the catalog.

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