Abstract 209 – The effect of season and latitude on the body mass of eight bear species in human care

Russell Van Horn, Anthony M Pagano, Mathias W Tobler

Many ursids exhibit significant changes in metabolism and body mass in response to
environmental and seasonal factors. In some ursids, these seasonal effects can include
extended and predictable periods of inactivity or torpor. In turn, those changes can affect the
timing of challenges to these bears’ management and conservation. Yet, in other ursids (e.g.,
sun bears, sloth bears), the existence or magnitude of such seasonality is poorly known. We
used records of body mass from eight bear species in human care within the Species360
Zoological Information Management System (ZIMS) to evaluate the effects of season and
latitude on overall body mass and change in body mass. This dataset encompassed 66,598
records from 1000 adult bears between 1980 – 2023 encompassing latitudes from -41 – 66°.
Andean bears in human care of both sexes exhibited significant decreases in body mass with
increasing latitudes (i.e., distances from the equator). Conversely, male Asiatic black bears and
female polar bears exhibited significant increases in body mass with increasing latitudes.
Female brown bears and giant pandas of both sexes exhibited significant increases in overall
changes in body mass across months of the year with increasing latitudes. Other species and
sex classes showed no relationship between overall body mass or changes in body mass with
increasing latitudes. These data provide insight into the capacity of different ursids to
seasonally vary their body mass and the influence of latitude on body mass. Additionally,
Andean bears exhibited the most pronounced sexual dimorphism in body mass, followed by
brown bears, black bears, and polar bears, with sloth bears exhibiting the least dimorphism.
Such variation in dimorphism across species may reflect sexual selection, leading to variation in
foraging requirements. Data from other bears in human care beyond Species360 would allow
us to more thoroughly evaluate the influence of season and latitude among ursids.