Looking at the dead "thing", I'd say it was neither fish nor bird.
The vertebrae are the wrong shape, and they're also too robust to be either IMO (birds have distinctive vertebrae to cut down weight as much as possible, and fish have spiny processes off the vertebral centrum).
The "skull" appears to be actually a pelvis, so it looks more like a heavily rotted mammal than anything else. It'll make good tadpole food in a few weeks whatever it is...