Accounting for viewshed area and animal availability when estimating density and recruitment of unmarked white-tailed deer

Quantifying demography of wildlife is vital to population monitoring;
however, studies using physical capture methods can prove challenging.
Camera traps have gained popularity as a density estimator tool in recent
decades due to noninvasive data collection, reduced labor, cost
efficiency, and large-scale monitoring capabilities. Many wildlife
populations are comprised of individuals with no unique natural markers
for individual identification, resulting in the need for unmarked
abundance models. The recently developed Space-to-Event (STE) model offers
a method for density estimation of unmarked populations using timelapse
photography. STE relates detections of animals to camera sampling area
(i.e., viewshed), resulting in density estimates that can be extrapolated
to abundance over large areas. Consequently, this makes STE sensitive to
estimates of viewshed area as small changes in viewshed could
significantly affect density estimation. Using STE, we estimated density
and recruitment of white-tailed deer (Odocoileus virginianus) in a densely
forested landscape using measurements of viewshed per camera. We compared
estimates of abundance derived from uniquely measured viewshed to
estimates of abundance derived from an assumed viewshed area held constant
across all cameras. When using a constant viewshed across all cameras, our
point estimates of abundance shifted away from uniquely measured viewshed
estimates in predictable ways, depending upon how much area was sampled.
Additionally, we demonstrated the need for further exploration of animal
availability at fine temporal scales by comparing estimates of density
derived from sampling the full diel period to estimates derived from
periods of peak activity (i.e., crepuscular periods). Finally, we extended
the usefulness of the STE model by using densities of fawns and adult
females to derive estimates of fawn recruitment.