I’ve heard anecdotes in which people complain that the sign people chose a bad place to tell the animals to cross. I can picture that happening, but have seen no direct evidence of it.
I can attest to requests for duck crossing signs, together with regrets that such signs are nonstandard and will therefore not be installed. The signs are nonstandard because the FHWA and Caltrans only have signs for animals large enough to mess up your car and possibly injure you. A line of baby ducks will not do that.