Weasels are very hard to keep out. They hunt mainly at night but some hunt during the day as well. The best protection from weasels is to surround the birds day yard with hardware cloth at least three feet high, attached to their normal day yard fence. Then two charged electric fence wires should be set up out side the fence. One wire should be about six inches off the ground and another at the top of the hardware cloth, about five inches out from the fence using stand off insulators. Remember that a weasel or mink can and do fit through a 1" diameter hole (about the diameter of a quarter) and if they get in, they will kill every one of the birds in the pen. Weasels are stealthy and are seldom seen, although you can rest assured that they are there. Weasels are known as neophobic, meaning they are afraid of new things. This fear will keep them away from a new pen for up to a year but they will eventually gain confidence and start killing your birds. Small birds must be locked up at night in a solid building with no openings bigger than an inch. Weasels are incredibly strong and very unpredictable. They are near impossible to trap because of there avoidance of new things (TRAPS) and are extremely territorial. Once a weasel establishes their territory they rule it with an iron fist. Only one weasel lives in a territory, they are not gregarious. This means once you have a weasel he is there to stay. They are not "just passing through" predators. I fear weasels more than any other predator because of there hunting abilities...though they prefer small birds like ducks and chickens, they will on occasion attack a full grown goose. Usually the goose will die of fright and stress from such an attack, but the burrowing wounds inflicted to the gooses chest (weasels will latch on and rotate their bodies leaving a gaping wound) can be serious and cause massive blood loss and eventual death for the goose.