I had a lone chick hatch and she was too tiny to be integrated with my bigger chicks so I gave her her own brooder and a buddy from the feed store. All was well for a few days until the buddy chick simply faded away and passed. She just got weak seemingly for no reason. I figured she just failed to thrive and returned to the feed store to buy buddy chick #2. He was healthy, eating, drinking and pooping normally. Today he went downhill in a matter of hours. He just got weak, lost interest in food, and passed away in my hands. He had no signs of paralysis or leg deformity. The catch is, all my other chicks including the tiny one I hatched are doing great. I keep a close eye on their temp, they all eat the same type of food, everybody is picked up and looked over every single day. They are housed within inches of each other. Sadly my tiniest baby is once again all alone. I don't want to buy another friend for her only to watch it die. Is there something I could be missing? Could a disease or parasite only affect the newcomers? My chickens are not vaccinated.