Hierarchical distance sampling, only some sites visited more than once

[Christina Hunt]

Hi everyone,

I have a distance sampling dataset with 200 sites, 120 of which were visited once and 80 of which were visited twice. I initially tried modelling this using gdistsamp but decided against it after reading a paper that suggested with two visits, I would need 450 sample sites to avoid huge errors in my parameter estimates (Barczyk, J., Kéry, M., Neubauer, G., Kellner, K.F., Soh, M.C. and Badia‐Boher, J.A., 2026. Performance of generalized distance sampling models with temporary emigration: a simulation study. Oikos, 2026(2), p.e11544.).

Instead, I ran a distsamp model and included site as a random effect on lambda e.g

distsamp(~1~Temperature+(1|Site),umf, keyfun="halfnorm",output="density", unitsOut = "kmsq")

I am trying to build my Bayesian modelling experience so I would like to try and replicate this analysis in a Bayesian framework, but I am a bit lost with how to do it. If I try to fit a temporary emigration HDS model in BUGS (section 9.5.4 of the AHM book), will that have the same issue as the gdistsamp model in that not enough of my sites have been surveyed twice? Is there a Bayesian alternative to running distsamp and just adjusting tlength so that sites visited twice have double the length?

Any advice or suggestions would be greatly appreciated!

Thanks,

Christina