Hello,
I have a mark-recapture data set for rattlesnakes with 89 adult individuals captured and marked over 2.5 years and I would like to estimate annual survival. Capture occasions occur at the den in the spring and fall so I have five sampling occasions: spring-fall-spring-fall-spring. Of these 89 individuals, 70 have no recaptures, 12 individuals have one recapture, 2 individuals have two recaptures, and 5 individuals have three recaptures. I know these small sample sizes and the short duration of the study make getting accurate annual survival estimates questionable but I was able to fit some simple CJS models (e.g., constant phi and time and/or sex dependent p). The best model had constant survival and sex-dependent recapture rates. My recapture rates are about 0.35 (± 0.10 SE) which is higher than what I’ve seen in other rattlesnake mark-recapture studies but not unreasonable. However, my annual survival estimates are about 0.38 (± 0.10 SE), which is much lower than I would expect for adult rattlesnakes. I would expect annual survival to be 0.70 or greater.
I have two questions. First, based on my sample sizes and short study duration is there any statistical reason to doubt the validity of these estimates? I know low recapture rates can bias survival estimates but are estimated recapture rates of 0.35 considered “low?” But biologically speaking we have no reason to suspect such low mortality. For example, in a concurrent radio telemetry study over this same time period, only one of 20 telemetered adults died. Second, could anyone provide suggestions for how I can use simulation to determine if I can reliably estimate annual survival given my sample sizes and study design? If I cannot provide the funding agencies with accurate survival estimates then the next best thing would be recommendations for a study design that can.
Thanks so much,
Javan