We had pretty good luck last year with the
fly predators from Spalding Labs. I don't think we ordered quite enough, as we did still have fly issues, but it was a lot less than in previous years.
with the birds, since I didn't want the chickens to eat the larvae, I would put them (the larvae) in containers out of reach of the birds until they all hatched. Directions say to sprinkle on the ground, but then I would have just had well fed chickens, not exactly what I was looking for
.
combined with some fly traps, some sticky tape, and manure management, we did okay last year. But, with the animals, it's always an ongoing battle.