Bobbi, predators are hard to predict. That they are! I went for several years without an attack, then 3 years ago, our dog died in June and we went on a 2-week vacation in July. My mom was letting the chickens out to free range in the morning, locking them up at night. She let them out one day, was over at noon for something or other, came back a few hours later and my rooster and 4 hens had vanished. The only sign of them was one feather from my rooster's tail. I'm guessing coyotes. It was the middle of the afternoon, but I think they figured out that there was no dog, and no humans present during the day. They got my chickens the day before we came home..You can go forever without a problem then suddenly something happens. Just because something can get in doesn’t mean it will. I’d think snakes getting into your coop through that 2x4 wire and into the coop to eat eggs even during the day is a much bigger threat than a weasel though if a weasel gets in it will cause more damage. I don't think we have any snakes here that would be a threat. I'm in west central MN, and the only snake I've ever seen is a garter snake. Never had one in the coop. The night time slaughter that I mentioned previously was a weasel. It killed about a dozen 6-week old chicks. No blood, no dismemberment or evisceration, just two little "vampire marks" under a wing or on the neck. Dead chicks scattered all over the coop. Worst part about that was, we had a visitor who had never been on a farm before and wanted to see some animals. I hadn't been to the coop yet that day, so I invited her to accompany me to do chores... Well, she got a taste of the reality of farm life.
Where are you keeping the chicks during the day and how long have they been there? Currently, the chicks are in a brooder in the coop. It's divided with the hens on one side, chicks in brooder on the other. Chicks are only a week old at this point. Another week or two, and I will remove the sides from the brooder and let them loose in their side of the coop. The hens will then be able to see them, and if I want, can make it so they can get right up to the dividing fence. Is your coop elevated? Coop is not elevated. Maybe a foot or so off the ground, but there are rocks for them to jump up on to get into the coop. I think they have been in that coop for a few weeks and that is a walk-in coop, much like mine. I don’t always use my elevated grow-out coop. Sometimes I just open the brooder door about the time they are five weeks old. It may take them a day or two to take themselves outside the coop but mine always come in that coop on their own at night. They will probably wait until the adults are on the roosts to come in, but they do come in. It’s never been a problem.
I have a separate juvenile roost lower than the main roosts and separated horizontally. Once they start to roost they use that, they are not going to go close to the adults on the main roost even though there is plenty of room. Before I put that juvenile roost in I had some try sleeping outside to stay away from the older bullies. I haven't integrated at such a young age before (except with a broody hen, and I let her take care of introductions and mean old biddies), but am guessing that the youngsters will go into "their" side of the coop to roost at night. I have some lower roosts set up on that side.
I’m convinced the reason I have problems in that grow-out coop is because it is elevated. I think they instinctively want to sleep in a group on the ground in some protected area until they start to roost. They have been too consistent over the years for me to believe anything else.