I had 1 chick get ill and recover, 1 got ill and died and one died suddenly. The 2 that died were 1 day apart. Here is my scenario: --Got 5 chicks on Feb. 12. They were 4 - 5 weeks old. Put them into a brand new coop which is 4 ft. x 6 ft made from non-pressure treated wood. They stayed inside the coop for a few days as they were afraid to come out. Floor of coop is lined with straw. Started running around their chicken yard, which is approx. 30 feet x 20 feet after a few days. There are some buttonwoods and native ground cover plants in their run(nothing that is on the "toxic to chickens" list). I am feeding them chicken mash, basic ration from the feed store, supplemented with a homemade mix of oats, millet, flax, coconut, bran, quinoa. When we had freezing cold weather a few times I closed up the coop and left them inside a little longer as it was warmer inside. --I keep water and dry mash in bowls inside the coop since they are inside all night and sometimes until mid-morning. I usually wait to let them out after I lock up the cats and I can be around to watch them since they are still fairly small. When they are outside I move the feed and water bowls outside. I have been giving them mealworms for treats, but not too many. --Around Feb. 20 one of the chicks was staying off to herself and not eating. We took her out of the flock and put her on extra mealworms, moistened mash and a heater on her crate. She got better within a few days. We put her back in the flock after 6 days and she is doing very well. --Last Wednesday, Mar. 4, another chick was acting lethargic and staying separate from the other birds. We took that chic out on Thursday to give it the same treatment, but it died within a few hours. --Last night I put all the chicks up around 6:00 p.m. and they all looked fine. We had spent a lot of time with them yesterday. They were still eating some moist mash when I put them up. I came downstairs at 8:00 p.m. and heard a noise in/around the coop. When I looked inside 3 chicks were huddled together and the 4th one was dead upside down next to the feed bowl. It was still very warm when I took it out so it must have just died. I suspected coxy based on what I have read, but I have not read that it causes sudden death. If anyone has any ideas on this I would love to hear it.