Estimating pre-harvest density, adult sex ratio and fecundity of
white-tailed deer using wildlife cameras
Abstract
Adult sex ratio and fecundity are key population parameters in
sustainable wildlife management, but inferring these requires estimates
of the density of at least three age/sex classes of the population (male
and female adults and juveniles). We used an array of 36 wildlife camera
traps during 2–3 weeks in autumn prior to harvest during two
consecutive years, and recorded white-tailed deer adult males, adult
females and fawns from the pictures. Simultaneously, we collected fecal
DNA (fDNA) from 92 20mx20m plots placed in 23 clusters of four plots
between the camera traps. We identified individuals from fDNA samples
with microsatellite markers and estimated the total sex ratio and
population density using Spatial Capture Recapture (SCR). The fDNA-SCR
analysis concluded equal sex ratio in the first year and female bias in
the second year, and no difference in space use between sexes (fawns and
adults combined). Camera information was analyzed in a Spatial Capture
(SC) framework assuming an informative prior for animals’ space use,
either (1) as estimated by fDNA-SCR (same for all age/sex classes), (2)
as assumed from the literature (space use of adult males larger than
adult females and fawns), (3) by inferring adult male space use from
individually-identified males from the camera pictures. These various SC
approaches produced plausible inferences on fecundity, but also inferred
total density to be lower than the estimate provided by fDNA-SCR in one
of the study years. SC approaches where adult male and female were
allowed to differ in their space use suggested the population had a
female-biased adult sex ratio. In conclusion, SC approaches allowed
estimating the pre-harvest population parameters of interest and
provided conservative density estimates.