Data from: Population dynamics of a long-lived pitviper inferred from capture-recapture data spanning four decades

Long-term studies of plant and animal populations are rare, particularly
for long-lived species with slow life histories. However, such studies are
necessary to understand how variation in vital rates affects population
dynamics. We used a large capture-recapture dataset spanning four decades
(1983–2019) to estimate several population parameters for adult females in
a metapopulation of a long-lived North American pitviper (Timber
Rattlesnake, Crotalus horridus) near the northern extent of the species’
geographic range. Apparent survival (ϕ, hereafter, survival) estimates
were variable (0.595–0.938) among years but generally high, whereas the
annual recruitment rate (f) was low (0.102, 95% confidence interval [CI]:
0.088–0.117). Survival increased by a quadratic function of the mean mass
of the adult female population, resulting in survival increasing with this
temporally varying population-level covariate until the population average
reached approximately 768 g; survival decreased with increasing mean mass
thereafter. The proximate causes of decreased survival for the largest,
and thus presumably oldest, snakes remain unknown but are likely related
to senescence and increased predation risk with advancing age. The best
predictors for encounter probabilities were the additive effects of color
morph (higher for yellow snakes than black snakes), sampling site, and
year. The model-averaged estimate of realized population growth (λ) was
0.992 (95% CI: 0.980–1.005). Removal of sampling variance from the
component of λ contributed by survival resulted in a 95% upper limit of
0.9997, indicating a declining population. Reflecting attributes of the
species’ protracted life history (late maturation, low fecundity, and
infrequent reproduction), the contribution of survival was on average 8.9
(95% CI: 7.6–10.4) times greater than the contribution of recruitment to
λ, representing the slowest life history documented for any snake
population to date. Our findings suggest management efforts to increase
adult survival, such as reducing mortality from anthropogenic factors,
should aid in the conservation of Timber Rattlesnakes and other imperiled
species with similar slow life histories.