It’s not uncommon for wild birds to have mishaps, or die when old and temperature-stressed. Weaker birds may succumb to diseases that would not be a problem for more robust birds. Also, many “teenaged” birds have accidents due to the newness of flight.
If you find a single dead wild bird:
Be sure to wear gloves or otherwise protect your hands when handling dead birds. Put the bird into a ziploc bag or other container, and dispose of it in a way that will keep other animals from being exposed to it. Incineration is a good option or you can place the bagged bird in with your everyday garbage as long as other animals do not have access to your trash.
If you find multiple dead wild birds:
Notify the state veterinarian immediately. He can approve shipping/testing at the state expense for diseases that would be a wildlife or public health concern.
If you find injured wild birds, including baby birds that may have fallen out of their nest, contact a licensed wildlife rehabilitation group. The Maine Department of Inland Fisheries and Wildlife maintains a list of wildlife rehabilitators.