Using a baby bottle to feed a baby pigeon (photo and description courtesy of Waynette from Pigeon Talk)
Using a baby bottle:
I use a small baby bottle and cut the tip of the nipple half way down (just enough to slide their beak into). Then cut the finger off a rubber glove and slide it over the nipple. Put a cross slit at the top of the glove (kind of surrounds their beak to help with the mess)
They love it!