This would be considered a trace fossil, also known as an ichnofossil.

Here's why:

* Trace fossils are not the preserved remains of an organism's body, but rather evidence of their activity.

* In this case, the footprint is a preserved trace of the bird's interaction with its environment.

Other examples of trace fossils include:

* Dinosaur tracks

* Worm burrows

* Fossilized dung (coprolites)

* Bite marks on bones

Let me know if you have any other fossil-related questions!