Is there a limit to the time contrast medium can stay in the warmer?
usually on the manufacturer information sheet should have storage requirements. I know for a fact Visipaque 320 can be in a warmer for 30 days once warmed to 98'. if it goes over it must be disposed of. when stored in regular temp 68-77 until expiration date.
Fat people have a bigger fat layer around their muscles, but they do not always stay warmer. Many "skinny" people are thin because they are quite fit and have a lot of muscle; muscles make you warmer. If the thin person is thin because they are just undernourished and in poor shape, then the fatter person will be warmer.
Birds will usually travel to a climate where it is much warmer. When birds do this it is called "Migration". Most birds will migrate to warmer climates, and the birds who don't will stay in the climate where they already are. While migrating birds will usually stay in a flock. The flock is usually in a V shape. The birds who stay will search for the food they can find in the habitat.