Why do bats always go out to hunt at night but not in the day?
The answer to almost all "why" questions about nature is: Because it works.
Most of the time we really can't say why a particular life style has evolved
for any creature. We can often figure out how it works. Over the course of thousands
of generations most species of bats have evolved special adaptations for hunting
at night, especially the remarkable "sonar" system they use to navigate and locate
prey. We know that it is a very successful adaptation because there are many species
and individuals of bats that use it, and it gives bats an advantage in that few other
creatures are competing for the abundant food offered by night flying insects. We
really can't say what all the selection pressures were that originally started bats
down that particular path.
My guesses are:
1) because of the cool night temperatures.
Bats are mammals and are warm blooded.
Flying requires a lot of energy and generates a lot of excess body heat.
So flying in the cooler temperatures at night helps the bats shed excess
body heat in the cooler night air.
This thought is re-enforced by their habit of roosting in dark cool caves
during the day.
2) Another reason is because a lot of insects come out at night, like
mosquitoes, fireflies, moths, and gnats.
3) Another reason is that the night air is cooler and has a higher density
than the hot air during the day, making it easier to derive lift by flapping
wings in cool, denser air.
Dr. Stewart has done some real thinking, and is right all down the line. Also,
keep in mind that bats have developed echolocation which allows them to navigate
at night, probably better than can be seen with their vision during the day. It is
safer to hunt at night for predators and competition for food are all but eliminated;
except of course with other bats.
Click here to return to the Zoology Archives
Update: June 2012