White-tailed Deer Distribution and Movement Behavior in South-Central Texas, USA

Authors: J.T. Beaver

Providing wildlife managers with reliable population abundance estimates for white-tailed deer (Odocoileus virginianus; deer) is challenging and requires proper evaluation of population surveys. My objectives for this study were to compare capture techniques (drop net, single helicopter, and tandem helicopter) and evaluate deer movement in response to infrared-triggered camera (camera) and spotlight survey methods in relation to potential biases associated with each method.

Cost and labor efforts were greater for drop nets than either helicopter method. All techniques were safe and effective methods for deer capture, but results showed tandem helicopter capture was superior for balancing cost-efficiency and safety while minimizing post-capture behavioral impacts.

I used movement data to determine if the presence and absence of bait altered deer distributions. For males, the use of bait detracted from percent canopy coverage, which was significant in determining deer distributions prior to the use of bait. This indicates the use of bait evoked a stronger response from males, violating the assumption of equal detectability during camera surveys. This pro-male bait-bias can ultimately result in an underestimation of female deer.

I conducted spotlight surveys based on road surface type and disturbance level due to traffic volume. More deer per area were encountered on unimproved (trails) and maintained gravel (gravel) roads than on paved roads, suggesting that deer either shied away from paved roads or congregated near trails and gravel roads. It is more likely deer shied away from paved roads due to high traffic levels resulting in density estimates biased low.

Behavioral change attributable to capture technique must be considered when selecting a capture method, and determining the period over which data are biased is critical to wildlife research. I recommend managers either not base harvest quotas on estimates obtained via baited camera surveys or be aware of the potential biases and try to account for underestimates of females and fawns. I also recommend managers either use road types with little traffic disturbance while maximizing visibilities, or incorporate an even distribution of non-overlapping transects for all road types present.

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