Using incidental mark‐encounter data to improve survival estimation

Abstract

1. Obtaining robust survival estimates is critical, but sample size limitations often result in imprecise estimates or the failure to obtain estimates for population subgroups. Concurrently, data are often recorded on incidental reencounters of marked individuals, but these incidental data are often unused in survival analyses.2. We evaluated the utility of supplementing a traditional survival dataset with incidental data on marked individuals that were collected ad hoc. We used a continuous time-to-event exponential survival model to leverage the matching information contained in both datasets and assessed differences in survival among adult and juvenile and resident and translocated Mojave desert tortoises (Gopherus agassizii).3. Incorporation of the incidental mark-encounter data improved precision of all annual survival point estimates, with a 3.4%-37.5% reduction in the spread of the 95% Bayesian credible intervals. We were able to estimate annual survival for three subgroup combinations that were previously inestimable. Point estimates between the radiotelemetry and combined datasets were within |0.029| percentage points of each other, suggesting minimal to no bias induced by the incidental data.4. Annual survival rates were high (>0.89) for resident adult and juvenile tortoises in both study sites and for translocated adults in the southern site. Annual survival rates for translocated juveniles at both sites and translocated adults in the northern site were between 0.73 and 0.76. At both sites, translocated adults and juveniles had significantly lower survival than resident adults. High mortality in the northern site was driven primarily by a single pulse in mortalities. 5. Using exponential survival models to leverage matching information across traditional survival studies and incidental data on marked individuals may serve as a useful tool to improve the precision and estimability of survival rates. This can improve the efficacy of understanding basic population ecology and population monitoring for imperiled species.

Survival of a small reintroduced griffon vulture population in the Apennines: Insights from Global Positioning System tracking

“…47 An increase in accuracy and precision of estimates could be attained both by increasing the sample of GPS-tagged vultures and integrating the data-set with information from multiple data sources, i.e., mark-resighting of ringed birds while at the feeding stations or in the wild, live recaptures, incidental samples and recovery of dead vultures. 51,62 Nonetheless, given the life span of the griffon vulture, 46 we emphasize the need for long-term studies, especially focusing on demographic and ecological processes. The long-term preservation of the griffon vulture is inextricably tied to our capability of mitigating current impacts and anticipating future ones, especially for small populations (such as those of the central-southern Apennines in Italy) of such a K-selected species.…”

Indirect impacts of a highway on movement behavioral states of a threatened tortoise and implications for landscape connectivity

“…This is an unusually high mortality rate for Mojave desert tortoises, who typically have annual survival rates between 0.90 and 1.00 64 – 66 . However, mortality can be dramatically higher (e.g., up to 40% mortality) in a single year irrespective of road proximity 54 , 67 . Because we intentionally focused on tagging tortoises near the highway, we are unable to determine if our high observed mortality was due to proximity to the highway 20 , was due to regional drought-based mortality factors 54 , an interaction of drought and proximity to the highway, or other unobserved factors.…”

Waif Gopher Tortoise Survival and Site Fidelity Following Translocation

“…Immature annual apparent survival in a wild-to-wild translocated population on a barrier island in Georgia was estimated to be 0.45 ± 0.26 in the first year following release and 0.84 ± 0.05 thereafter (Tuberville et al 2008). As with many other chelonians, including the Mojave desert tortoise, gopher tortoises have lacked reliable survival estimates for distinct stage classes (hatchling, juvenile, subadult) and instead relied on aggregate estimates for immature classes (Brand et al 2016, Harju et al 2020). To accurately model population dynamics and trajectories, stage-specific survival estimates are essential (Smith et al 2006, Tuberville et al 2009).…”