McLoughlin Lofts recommends using a Moxidectin wormer such as Quest (marketed for horses) for pigeons and doves.
From their site:
"Quest is a gel that must be mixed in a blender poured into the water and given to the pigeons for 24 hours. It lasts in the pigeons system for 30 days. Not only does it eliminate all internal intestinal worms, it eliminates gape worms and all external parasites. We treat the race team with Quest seven days before a big race and have only had super results.
We place 1/2 tube of Quest in one cup of water in the blender. We blend for 30 seconds and then pour this into 4 gallons of water and stir."
If it's good enough for a $100 pigeon, it's good enough for my ferals and chickens.