Nocturnal Animals

Nocturnal animals — those active primarily at night — have evolved a remarkable suite of adaptations for low-light environments: enlarged eyes with high rod:cone ratios (owls' eyes so large they cannot rotate, so owls turn their whole head up to 270°); tapetum lucidum (reflective layer behind the retina that doubles available light — the 'eyeshine' of cats and nocturnal mammals); echolocation (bats, shrews, some birds); enhanced olfaction (most nocturnal mammals); and heat sensing (some snakes). Bats are the most species-rich nocturnal group — 1,400 species comprising 20% of all mammal species. They are the world's primary nocturnal aerial predators of insects (a single little brown bat eats 600-1,000 insects per hour) and crucial pollinators of many tropical plants (including mangoes, bananas, durians, and agaves — the source of tequila). White-nose syndrome (a fungal disease) has killed 7 million North American bats since 2006, threatening agricultural systems that depend on insect control.