I got a new banty roo, locked him in a pen with the banty girls for a few days before bringing him into the flock. On the first night of mingling with the whole flock he defaulted to the pen he was in while everyone else (including his girls) roosted in the main coop. So he was alone all night, didn't even roost in the coop, just sat on top. I found him slumped forward in the morning with a purple comb. I snuggled him in under the heat lamp for a few hours and when his comb turned red again and he stopped shaking I put him back out. Found him that night again slumped forward and shivering. So he spent last night, all night, in the brooder room under a lamp. I got him some sugar water and made sure he ate. He finally perked up and made a mess in the house so I put him back out. He's been slow but keeping up with the flock today. I put him on the roost tonight (cause he defaulted to old pen) and when I came out to shut the coop well after dark he was on the ground under the perches, slumped forward. So he's now back inside, sitting in my lap with a full crop of hot burnin' scratch and water. He's eaten and drinken very well. He's become thin as a rail in the last 72 hours. His comb keeps fluctuating between normal red and deep purple in some parts. He feels warm but is still shivering. I will keep him inside until he's 100% again. But thoughts on what's wrong? What more I can do? None of my other 25+ birds are acting ill in any way. Hhe came with 4 other banty boys, all brothers, and the others are all ship-shape and surviving the cold in their roo pen.