pigeons raiding food dish

Yep, I've got the same problem with not only pigeons but mallards as well. Think the mallards are a bigger problem than the pigeons.

Now i can only feed pellets at night in the house.  We put enough in the troughs for when they wake up and they have to make do during the day.
 But they dont go short as they are all free ranging through the cattle yards all day and pick up no end of feed and bugs from the straw and muck.
I use to put the feed troughs up on the dropping board during the day but the mallards have found them now so we cant even do that any more.
On the plus side, I only have to say 'DUCKS' to the dog and she belts of and puts them all up.