My roof line faces directly south, so it gets the full brunt of the hot
summer sun. When it's cooler, the bats align themselves in the direction of the eaves/gutter,
literally cramming themselves into the "V" as closely as they can. They screen themselves with
a wing, much as Bela Lugosi did in the Ed Wood films. As it warms
up, and the metal gets hot, the bats align themselves at right angles to the eave line as seen
here. When it gets too hot, they might roost on the northside eaves. I think that the bats shown
the very common Little Brown Bats.
Check out Bat Conservation International
for information about bats and about the efforts to save them worldwide.