How common is thermal vision?

Do cats and owls have thermal hot-spot detection?

The best way to find out if predators have thermal hot-spot detection is animal behaviour experiments. These should consist of small vole-sized lures at a temperature of at least 35 degrees centigrade in known hunting grounds of cats and owls. If owls and cats show the ability to sense these lures the most likely infrared sensor anatomy is a modification of the retina. The cornea, vitreous humor and optical retina are transparent at 10 microns wavelength and an infrared sensor would look like an enervated membrane with a thickness of 1.6 microns in an air filled cavity  behind the retina. Such a structure might necessitate an immovable eyeball.