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Bats: our flying bug zappers

These summer nights are warm and calm. They are very alive with all sorts of critters. The usual nocturnal rabbits, porcupines, foxes and deer move about and feed now.

These summer nights are warm and calm. They are very alive with all sorts of critters. The usual nocturnal rabbits, porcupines, foxes and deer move about and feed now.
Owls call and search for meals at this time, too.
Good numbers of insects, like moths and beetles, silently go about their business, while crickets and katydids add sounds of courtship and territory proclamations to the darkness. Meanwhile, the opportunistic spiders gather plenty of midnight snacks.
Others out feeding at this time do so on the wing. Bats, the only flying mammals, come out each night at dusk and spend several hours gathering a bellyful of bugs.
Seven species have been recorded in the Northland. They range from the large silver-haired bat to the tiny eastern pipistrel. Others include the red bat, hoary bat, northern bat, big brown bat and little brown bat. Some roost in trees and rarely make use of human dwellings, while others are often in our buildings. A few are social, living in colonies, others are loners. But all have one thing in common -- they feed on large numbers of insects each night.
On some evenings and nights, this may translate into more than 1,000 mosquitoes per bat.
Such feeding frenzies usually happen during the dark hours and without us seeing their predation. Insects selected besides mosquitoes include moths, midges and any other night-flying bugs that happen to be available.
Food is found with the use of a system called echo location. Sounds sent out bounce off the flying insect and come back to the bat, telling the location of the food. The flying predator is able to find and dine. Huge ears allow this system to work.
Eyes are small, but bats can and do see.
Most of us usually encounter only two kinds of these bats: the big brown bat and the little brown bat. Both regularly roost in buildings during the day and leave at dusk to feed -- often over lakes, ponds and rivers. After nocturnal meals, they return to their shelter by dawn.
These flying bug zappers have been active since spring, but now in August, bats become more energetic. In late summer, bats go through mating rituals. Their nightly flights take them to caves, mines or buildings where they gather in large flocks for mating before the chill of autumn sends them on scattered migrations.
Though mating occurs in late summer, fertilization does not happen until next spring. Females are able to store viable sperm throughout the winter. After a gestation of 50 to 60 days, they give birth in June.
Most of the Northland bats will soon be migrating or going into a winter shelter. Through the cold times they enter a torpid state that is similar, but not identical, to hibernation. Some winter movement does happen, but not enough to use up the valuable stored food that allows them to survive until spring.
With a limited number of bat species in the Northland, it may be a bit of a surprise for us to know that bats are widespread and very common throughout the world. About 20 percent of all kinds of mammals are bats, nearly 1,000 species.
These August nights may be the best time of the year for us to see the kinds of bats living here.
Larry Weber is author of the "Backyard Almanac." He lives in Carlton County and teaches natural science at Duluth's Marshall School.

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