Charlotte Kingan, of Ardgowan School, asks :-
Why do merino sheep stand in a huddle in the hot, hot sun?
David Lindsay, a sheep scientist at the University of Western Australia, responded.
Merino sheep only have a few sites in their body that affect temperature regulation. The head is one and, in rams, the scrotum is another. (We do an experiment with our students in which we use a hessian tube with hot air to heat only the testes of rams and record their response. They pant more [no surprise] but they also lose body temperature. The input to the testes is less than the stimulated output from the lungs. If we heat an equivalent surface of, say, the leg there is no panting response and a slight rise in the body temperature. )
So if the head is in the shade, the animal thinks that it is cool or at least as cool as if the whole animal were in the shade. If you observe the animals in a huddle you will note that the one thing they have in common is that their heads are always in the shade of other sheep. In reality, they are not so silly because with 50mm or so of wool insulation they don't get a lot of the radiant or convected heat to their bodies anyway.
It makes a good story and it is probably more or less correct.