B6

Elizabeth Walsh - Nature Notes

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Like all other mammals, bats give birth to live young, produce milk to feed their young and are warm blooded. Unlike all other mammals, bats can fly. They have long slender fingers, extended arms and a short tail, all of which are joined by a fold of skin, much like a thin membrane, that forms their wings.

People with poor eyesight are often referred to as being "as blind as a bat." However, this phrase could not be further from the truth, as bats have very good eyesight. This false statement probably come from the fact that bats do not hunt by sight, but by echolocation. With echolocation, a bat sends out a high frequency signal. When this signal hits a prey item, such as a moth, the signal will bounce off the prey and come back to the bat. From this, the bat will be able to detect the exact location of the insect. As an adaptation to pick up the signals more clearly, bats have extremely large ears that pick up a variety of signals, much like a satellite dish. As well, some moths have adapted to detect the signals of bats and in turn will send false signals back to the bats to evade detection.

There are 19 species of bats found in Canada, with the most abundant and widely distributed being the little brown bat. The little brown bat weighs only 8 grams and has a wing span of 22 cm. In flight, this bat, like the others, looks larger than at rest.

Astonishingly, a bat has a long life span of 30 years, much longer than other mammals of the same size.

During the winter months, bats carry out a combination of migrating and hibernating. The little brown bat will migrate hundreds of kilometers to adequate hibernation sites. Bats will hibernate in underground caves and in buildings. Migration from Canada occurs when the weather becomes harsher and insects are not available for food.

Mating occurs just before the commencement of hibernation. The female will store the sperm in her uterus throughout the winter months. In spring, when the female leaves her hibernation site, ovulation and fertilization will occur. While pregnant, a female will make her roost during daylight hours in the warmest area possible. These roosts will often be comprised of hundreds of roosting pregnant females.

After 50 to 60 days of gestation the young are born and will be nursed at these roosting sights. Only one baby will be born to a female. At night the female will leave to feed and on returning she will be able to determine which baby is hers from the hundreds at the location.

By 18 days of age, the young bats will be able to fly. At this time they will change from milk feeding to eating insects like their mother. Males are not present at the nursery roosts, and their parenting role terminates after the donation of the sperm.

Bats eat many different insects, including moths, beetles, mayflies and midges. During one night a bat will eat 50 to 100 times their body weight in insects alone. Bats capture their food in flight. Instead of capturing their prey in their mouths, they entrap the insect in the membrane of their wing or tail and will then transfer it to their mouth. Little brown bats can capture as many as 10 insects in one minute.

Elizabeth Walsh is a Miramichier and knowledgeable about all things natural. She shares her love of Canada's plants, animals and birds in this column.