Got to go with Mink, They can squeeze through the smallest hole and just keep killing till every bird is dead. Plus they like to pile them all up in a corner. I have a totally enclosed chicken coop and run. And still have had 3 huge losses to the Mink.
Dogs would be close second, and are #1 if they are owned by a neighbor who is neglectful and ignorant. Had a couple bad dog experiences, but each time the neighbor has been very sorry and considerate.
Raccoons would be a distant #3, they are crafty and had some bad experiences with. 1 Time they pulled my baby ducks through the cages to get them and all I had left was just heads and feet in the cage. But have to give them some respect as they normally only take what they need and won't clean out your whole flock in a night if they get in.
For Pigeons
- Hawk is #1 since they attack in the day, right in front of you and are protected
- Weasel is #2 basically a smaller version of the mink.
A friend of mine has issues with corn snakes. She has found one right in the nest with an egg in his belly then one nearly killed her giant roo. It had constricted around the rooster nearly crushing him. She rescued the bird and nursed him back to his old self. I didn't think a corn snake would take on such a big rooster.
We have had run ins with hawks and possums, but by far I have had the most problems with neighborhood dogs. Pets strays...you name it. I have also seen a ton of people lose hens to their family dog. I have to say dogs have got to be the worst if only because of the amount of dogs out there and their lack of fear of humans...
noticed some people saying you can't do anything about hawks because they're protected.
They're protected over here too, but it is legal to set a hawk trap, to protect your flock as long as you set it within your "chicken farm".
I personaly hate foxes with a passion. I didn't like the way that the where hunted in the UK with the many dogs and horses, but I have no problems about thinning the numbers down.
All in all myself and other poultry keepers in the area lost over 150 birds to a fox last year.