Tile mastic or liquid nails applied. Smooth over with a little bit of water. Let dry. Check appearance of patched area. If it needs more mastic or liquid nails do over again. The mastic or nails may shrink so thats the reason for a second coat if needed.
If I had to repair a decoy like this I would repair, prime over existing paint and then repaint the whole decoy with my favorite flavors.
But thats just me.