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The retinas of most mammals contain two types of photoreceptor cells, the cones for daylight vision and colour vision, and the more sensitive rods for night vision. Nocturnal bats were traditionally believed to possess only rods. Now scientists at the Max Planck Institute for Brain Research in Frankfurt and at The Field Museum for Natural History in Chicago have discovered that nocturnal fruit bats (flying foxes) possess cones in addition to rods. Hence, fruit bats are also equipped for daylight vision. The researchers conclude that cone photoreceptors might be useful for spotting predators and for social interactions at periods of roosting during the day. Flying foxes often use exposed treetops as daytime roosts, where they assemble in large colonies (Brain, Behavior and Evolution, online May 2007).
The mammalian order bats (Chiroptera) has two suborders, microbats (Microchiroptera) and fruit bats or flying foxes (Megachiroptera). In contrast to microbats, fruit bats (Fig. 1) do not echolocate. They have large eyes and pronounced visual centres in the brain. Fruit bats need a good sense of vision, because when they forage at night for nectar and fruit, they orient by vision and the sense of smell. During the flights to the foraging grounds at dusk and the return to the daytime roost at dawn, the animals navigate solely by vision. On moonless nights, fruit bats cannot fly and stay hungry. Visual navigation at twilight and sometimes also during the daytime did not fit the older view that fruit bats only possess rods, the photoreceptors for night vision. This prompted Brigitte Mueller and Leo Peichl of the Max Planck Institute for Brain Research in Frankfurt/Main and Steven Goodman from The Field Museum for Natural History in Chicago to study the photoreceptors of fruit bats with modern histological methods
Contact: Dr. Brigitte Mueller