Abstract:
Little is known about Columbian black-tailed deer (Odocoileus hemionus
columbianus) because of their elusive nature and the logistical difficulty of
studying them in densely forested and mountainous terrain. The Oregon
Department of Fish and Wildlife has identified fawn survival as an important gap in
the current knowledge of demography and their understanding of an apparent
population decline.
We used vaginal-implant transmitters to locate birth sites and capture
newborn Columbian black-tailed deer fawns in the Umpqua National Forest in
western Oregon. We used modified Clover traps to capture deer during the winter
and early spring of 2000 and 2001. Vaginal-implant transmitters were inserted into
36 adult does in 2000 and 32 adult does in 2001. We identified a total of 42 birth
sites within our study area using this technique and we captured 23 fawns which we
monitored daily throughout the summer.
We modeled birth site selection by examining both site-specific variables
and characteristics that describe habitat structure across a nested, hierarchical range
of four circular areas. We used logistic regression to compare 42 birth sites with 80 random sites. The model that explained the most variation included the amount of
edge and the average slope within 1,000 m of the birth site.
We radiocollared 23 fawns from 2000 and 2001; 19 were captured at the
birth site, which was identified using the vaginal-implant transmitter, and 4 were
captured opportunistically. Fawns were located at least every other day and we
assessed habitat selection using selection ratios. Fawns used open and shelterwood
patches more than their availability in the study area. Timber habitats were used
most by fawns, but were used less than available.
Survival was monitored daily from the fawns estimated date of birth to 76
days. The Kaplan-Meier survival estimate for 76 days was 44% (95% confidence
interval=23-66%). We fitted our survival data to the Weibull distribution and took
an information-theoretic approach to construct a priori models using fawn capture
morphometrics and habitat variables within a 600 m and 1,000 m radius of the
capture site. The model that best explained fawn survival time was the amount of
roads within a 1,000 m radius of the capture site. A higher road density within
fawn summer range increases fawn survival time by likely minimizing predator
density due to vehicular disturbance.
