I found most of my bird bones in a large parking lot that has a lot of nesting spots for birds like pigeons and starlings another good spot to find dead birds is under large windows as they tend to fly into the windows and die
If you found a carcass you can take it into the woods and allow it to rot (time may vary) for small animals expect about 3-6 days for larger animals expect around 2-3 weeks I personally would leave them for a month or so
