Camera traps seem to be the latest vogue, and may prove themselves broadly useful. If there are few enough individuals, each can be identified and enumerated. But otherwsie, hard to get actual densities. Likewise, within a season, within a species, and within a habitat, dung counts may be more reliable than other survey techniques for relative numbers, but translating to absolute densities is troublesome. If costs can be kept down, DNA fingerprinting may also be a fun way to enumerate (using dung, most likely).

Absolutly agree with Truman. Camera traps could be useful, but usually you will need more information. State of the art analytical inference-based procedures to estimate densities using spatially explicit frameworks - linking abundance with location by estimating a latent variable representing the individual’s activity centres - such as spatial capture-recapture (SCR), spatial mark-resight (SMR) and spatial count (SC) approaches, can be implemented even with species without marks (SMR, SC), but in these cases you need to combined with different sampling methods (eg, telemetry or marking a small sample of the populaton).

If you can genotype your samples and use SCR, you will be able to make better inferences about the population sizes (and densities).

Regards,

Jose

eDNA? Was at a conference recently where a delegate had been looking for fish in ponds using DNA but ended up detecting all kinds of terrestrial animals as well because they came for a drink.

I agree that camera traps are being used more for monitoring species. There is an excellent review of the use of camera traps and suggestions on how to overcome problems utilizing camera traps for monitoring by Burton et al. 2015. 

Burton, A. C., E. Neilson, D. Moreira, A. Ladle, R. Steenweg, J. T. Fisher, E. Bayne, and S. Boutin. 2015. Wildlife camera trapping: a review and recommendations for linking surveys to ecological processes. Journal of Applied Ecology, 52:675-685.

I think this will largely depend on the species of wildlife you want to estimate the population. For camera traps, it will require you to identify the most used animal tracks, resources such as water points, mineral licks, feeding points etc. This may not be that easy in a forest e.g tropical forests. This is why a combination of the old techniques such as "call-back methods", ;;dung methods'', capture and recapture methods are still relevant in many parts of world where wildlife is still abundant.