In my view camera traps may be best used for detection of presence/absence of crocodiles and/or their behavioural studies rather than strictly abundance estimates:

https://www.researchgate.net/publication/311614241_Employing_Camera_Traps_for_Studying_Habitat_Use_by_Crocodiles_in_a_Mangrove_Forest_in_Sarawak_Borneo

http://41.77.4.165:6510/www.pressesagro.be/base/text/v18n3/446.pdf

Thanks Dr Nyirenda for your suggestion!

You are most welcome!

If you can uniquely identify your animals in the images, then there is a large body of literature on spatially explicit capture recapture which provides a solid framework for estimating animal density (in a spatially explicit way, potentially as a function of additional covariates) - The following reference provided a good soft introduction to the topic

Borchers, D. L. 2012 A non-technical overview of spatially explicit capture-recapture models Journal of Ornithology, 152 , 435-444

and this second one (is one of many examples that) provides details about camera trap studies:

Tobler, M. W. & Powell, G. V. 2013

Estimating jaguar densities with camera traps: Problems with current designs and recommendations for future studies Biological Conservation, , 159 , 109-118

This will work for crocodiles or any other species that can be uniquely identifianble from the photos. A diferent approach would be using distance sampling related approaches, and those are described here for camera traps:

Howe, E. J.; Buckland, S. T.; Després-Einspenner, M.-L. & Kühl, H. S. 2017.

Distance sampling with camera traps Methods in Ecology and Evolution, 2017

Finally, I don't know the deatils about this one, but the title suggest it might be what you need if individuals can't be identified uniquely - this will possible require some strong assumptions

Nakashima, Y.; Fukasawa, K. & Samejima, H. 2017

Estimating animal density without individual recognition using information derivable exclusively from camera traps Journal of Applied Ecology,

Hope it helps!

Thanks so much for your answer. As you already mentioned, spatially explicit capture and recapture methods can be applied to the population that is individually identified or cannot be identified too . I am wondering if I can find the studies which already applied that models for crocodiles population estimation from camera traps data. Thank you very much for your useful references!

Hi Kay,

I am studying parental care on crocodilians nests... right now I'm searching the best equipment based on cost-benefit. Do you have some suggestion about the models of cam trap?