Hmm...

birds are more sight oriented than smell oriented.

Some people have excellent senses of smell, most don't (and some have almost no sense of smell). Probably something similar is true of animals whose typical sense of smell is better than humans.

Note that having a sensitive sense of smell should also be a weakness in some contexts.

And then there's the "fade out with time" issue. Plus, to do it right, there'd have to be effects from perfume, rotting corpses and so on.

Finally, I think the results you're proposing are far too specific. There's already blood trails which accomplish the bulk of what's probably reasonable.

It might be plausible to introduce some utility form with this as its utility ability, but I suspect this involves way too much work for the gain.