Data from: Decadal heat and drought drive body size of North American bison (Bison bison) along the Great Plains

Large grazers are visible and valuable indicators of the effects of
projected changes in temperature and drought on grasslands. The grasslands
of the Great Plains has supported the greatest number of bison (Bison
bison; Linnaeus, 1758) since prehistoric times. We tested the hypothesis
that body mass (BM; kg) and asymptotic body mass (ABM; kg) of Bison
decline with rising temperature and increasing drought over both temporal
and spatial scales along the Great Plains. Temporally, we modeled the
relationship of annual measures of BM and height (H; m) of 5781 Bison at
Wind Cave National Park (WICA) from 1966 to 2015. We used Gompertz
equations of BM against age to estimate ABM in decadal cohorts; both
females and males decreased from 1960s to 2010s. Male ABM was variable but
consistently larger (699 vs. 441 kg) than female ABM. We used local mean
decadal temperature (MDT) and local mean decadal Palmer Drought Severity
Index (dPDSI) to model the effects of climate on ABM. Drought decreased
ABM temporally (˗16 kg/local dPDSI) at WICA. Spatially, we used
photogrammetry to measure body height (H) of 773 Bison to estimate BM in
19 herds from Saskatchewan to Texas, including WICA. Drought also
decreased ABM spatially (˗16 kg/local dPDSI) along the Great Plains.
Temperature decreased ABM both temporally at WICA (˗115 kg/°C local MDT)
and spatially (˗1 kg/°C local MDT) along the Great Plains. Our data
indicate that temperature and drought drive Bison ABM presumably by
affecting seasonal mass gain. Bison body size is likely to decline over
the next five decades throughout the Great Plains due to projected
increases in temperatures and both the frequency and intensity of drought.