Point taken.
The more I think about it, the more I feel @henrydelange has hit the nail on the head.
Two new drop-down fields are needed:
1) “Alive”, “Dead”, or “Uncertain”.
2) “Present at the moment”, or "Evidence of past presence"
If the user selects Evidence of past presence, it would be beneficial to allow them to select “Tracks”, “Excrement”, “Feathers” etc etc from a drop down list.
Recording such data would allow people who have particular expertise in identifying animal tracks to run a filtered search for these sorts of observations.