Influence of thermal cover on habitat selection by male white-tailed deer

Background/Question/Methods

Forage availability and nutritional quality are commonly driving factors in habitat selection by Cervids.  However, thermal cover has been implicated to influence habitat selection in subtropical and semiarid climates with hot summers.  We hypothesized that habitat selection by male white-tailed deer (Odocoileus virginianus) during midday in summer is driven by availability of sites with low operative temperatures and taller woody canopy height rather than screening cover, forage crude protein, and forage standing crop.  Operative temperatures were estimated using blackglobes that were constructed using 15cm diameter copper balls.  Fifty one blackglobes with temperature sensors were randomly placed within 10 vegetation communities throughout the 1,367 ha study site and recorded temperatures every 30 minutes.  Six male white-tailed deer were captured in autumn 2007 and 8 male white-tailed deer were captured during autumn 2008.  All deer were fitted with Lotek 3300L global positioning system (GPS) collars that acquired locations every 30 minutes.  Vegetation heights were measured using light detection and ranging (LIDAR) imagery.  Forage standing crop and screening cover were estimated along 109 transects within the study area during each summer.  Crude protein samples were collected from forage plant species in the summer of each year.  Data were analyzed using case controlled logistic regression. 

Results/Conclusions

During  summer 2008, the odds of a male white-tailed deer selecting a specific location during midday decreased 6% for every 1 g/kg increase  in crude protein (P < 0.001), decreased 0.7% for every 1°C increase in operative temperature (P = 0.023), increased 16% for every 5% increase in screening cover (P < 0.001), and were 1.6 times more likely to select vegetation with taller vertical canopies for every 1m increase in canopy height (P < 0.001).  During summer  2009, the odds of a male white-tailed deer selecting a specific location during midday decreased 66% for every 5 g/0.25m² increase in biomass,  increased 5% for every 1g/kg increase of DM in crude protein (P < 0.001), decreased 1% for every 1°C increase in operative temperature (P = 0.017), and were 1.64 times more likely to select vegetation with taller vertical canopies for every 1m increase in canopy height (P < 0.001).  Availability of lower operative temperatures in microhabitats with taller woody vegetation is one of the driving factors in habitat selection during midday by male white-tailed deer; however, forage nutritional quality and availability appear to be the primary factors in habitat selection even in torrid environments.