White-tailed deer movement in response to helicopter surveys

Disturbance of wildlife from aircraft during aerial surveys could affect behavior or displace animals, causing them to cross multiple transects resulting in double counting or increasing likelihood of them seeking cover thereby impacting detection probability. We monitored 14 GPS-instrumented male white-tailed deer (Odocoileus virginianus) during helicopter surveys to evaluate if surveys influenced behavior. We collected GPS locations at 10-min intervals during helicopter flights (i.e., 0700-1000 hours) and determined which individuals were contacted (i.e., within the flight transect at the moment of flyover whether detected or not) by the helicopter. We evaluated activity rates (% of seconds active during 10-min fix interval) and movements (m) of contacted and non-contacted deer using generalized linear mixed effects models (GLMMs) and habitat selection using step-selection functions (SSFs). Activity rates of deer did not differ between contacted and non-contacted individuals, however, contacted deer had shorter step-lengths. There was no difference in selection of vegetative cover between contacted and non-contacted individuals. Deer that were in close proximity to helicopter flyovers (i.e., 100 m on either side of the aircraft) reduced their step-lengths, potentially decreasing detection probability. We found no evidence that disturbance from helicopter flyovers result in deer altering habitat selection or fleeing in a manner that could result in double counting. Instead, it appears deer disturbed by surveys are more likely to reduce movement.