Pigeons dont sweat they have no glands for that. However i dint think it matters if you can part the keek feathers easily or not. I think it down to the temp in the loft and outside in the summer months. I think their easier to part at that time and the birds are in condition and hopefuly form. I have parted the feathers around the keel a few days before basketing and they have still came up trumphs so i dont think it matters.