https://doi.org/10.1093/aje/kwx077
https://doi.org/10.1097/01.ede.0000135174.63482.43
https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3689437
Mark-recapture, distance sampling, etc. Hard to find approachable papers on these topics.
https://distancesampling.org/whatisds.html
https://doi.org/10.2307/1939816