Capture method affects survival estimates and subsequent interpretation
of ecological covariates for a long-lived cervid
Abstract
Understanding what variables affect ungulate neonate survival is
imperative to successful conservation and management of the species.
Predation is commonly cited as a cause-specific source of mortality and
ecological covariates often influence neonate survival. However,
variation in survival estimates related to capture methodology has been
documented with opportunistically captured neonates generally displaying
greater survival than those captured via aid of vaginal implant
transmitters (VITs), likely because of increased left truncation
observed in the opportunistically captured datasets. Our goal was to
assess if 3- and 6-month survival estimates varied by capture method
while simultaneously assessing if capture method affected model
selection and interpretation of ecological covariates for white-tailed
deer neonates captured from three study sites in North Dakota and South
Dakota, USA. We found survival varied by capture method for 3-month
neonate survival with opportunistically captured neonates displaying up
to 26% greater survival than their counterparts captured via VITs;
however, this relationship was not present for 6-month survival. We also
found model selection and subsequent interpretation of ecological
covariates varied when analyzing datasets comprised of neonates captured
via VITs, neonates captured opportunistically, and all neonates combined
regardless of capture method. When interpreting results from our VIT
only analysis for 3-month survival, we found survival varied by three
time intervals and was lowest in the first two weeks of life. Capture
method did not affect 6-month survival which was most influenced by
total precipitation occurring during 3 – 8 weeks of a neonate’s life
and percent canopy cover found at a neonate’s capture site. Our results
support previous research that capture method must be accounted for when
deriving survival estimates for ungulate neonates as it can impact
derived estimates and subsequent interpretation of results.