I'm not an expert in this field, but have been doing some self study for a local project... Resolving animals in an image is not purely height related - but rather a combination of height and focal length (distance between the camera lens and the image sensor) (with some other factors) - Ground Sampling Distance (GSD) or Spatial Resolution is often used interchangeably (but there are slight differences). Flying low with a wide angle lens, or high with a telephoto lens can have the same GSD... 

See the following for general discussions of GSD (and how to calculate it) vs Spatial Resolution:

• https://www.propelleraero.com/blog/ground-sample-distance-gsd-calculate-drone-data/ or
• https://support.pix4d.com/hc/en-us/articles/202559809-Ground-sampling-distance-GSD-in-photogrammetry or
• https://www.researchgate.net/post/Whats-the-difference-between-pixel-size-and-grid-resolution

I don't know much about the use of LIDAR for identifying animals but this seems a very interesting article to start with: https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/2041-210X.12219

As to what GSD/Spatial Resolution is needed: it depends on the animal size. It seems that 0.5cm GSD is best to recognize cattle size animals (www.sciencedirect.com/science/article/abs/pii/S0168169922000060), but elephants have been identified at 31 cm resolution in South Africa using satellite data (https://zslpublications.onlinelibrary.wiley.com/doi/full/10.1002/rse2.195). 

For comparison, Google Earth images generally range from 60cm GSD and up to 20+m, depending on location (https://gis.stackexchange.com/questions/11395/spatial-resolution-of-google-earth-imagery).

Another pratical issue to deal with is that animals move - especially move fast when disturbed by low flying drones - and it could cause significant estimation issues.

Now if we can get 1cm GSD satellite images of large areas it would be REALLY helpful :-)

As an aside, my ideal scenario is to eventually replace current plane/helicopter based animal surveys with automated options. My specific study area is about 25000ha / 250km2 / 62000 acres, and 3 helicopters (with trained personnel) takes a full day to count animals - at a fairly high cost in local currency (ZAR 250k quoted). I had one estimate to do a image based survey with LIDAR, and just to image this large area at approximately 3cm GSD will take approximately a week of plane flying time for about the same cost...