Little Brown Myotis

Bats are the only mammals capable of true flight.

There are over 25 species of bats in the Pacific Northwest and California. Except for a couple tropical species found in Southern California, all these bats are insectivores and mostly nocturnal.

In the bat, the hand bones have been modified into wings. A vestigial “thumb” is located on the leading edge of the wing while the four long bones support the wing. A nearly hairless membrane spreads between the elongated “fingers” of the hand, between the wings and hind legs and in some species between the hind legs and the tail.

Bats orient by echolocation. Bat ears are well developed and have a fleshy tragus (projection) at the ear opening. The tragus is believed to play a role in vertical sound location. Bats emit a series of high frequency sounds which strike objects and are “echoed” back. Bats can fly in total darkness without hitting objects as long as their ears are not covered or obstructed. In addition to avoiding obstacles, echolocation assists bats in locating prey insects which they eat while flying. The eyes of bats are small and are not used for orientation.

Bats adapt to a lack of insects in winter by migrating out of their summer range or by becoming dormant and hibernating during the winter. Flying has a high metabolic cost. The daytime temperature in some bats, while they are at rest, approximates the ambient temperature (diurnation). This strategy reduces metabolic processes and conserves energy.

The high metabolic demands of flight require that bats consume about half their body weight in insects each night. A lactating female must eat more than her entire body weight each night.

Other than man bats have few enemies. Owls and snakes eat a few. Interestingly large trout will catch small bats while they drink or while the bats are skimming over the water in search of insects. Domestic cats also learn to catch bats.

Bats are difficult to distinguish and identify, particularly on the wing. Leonard recently found a dead bat near his veterinary clinic (Lookout CA) and we were able to examine it. It appears as though its wing was broken. I believe this specimen is a little brown myotis or a little brown bat. Little brown myotis are from 60 to 102 mm in length (the body in this case was 75 mm long). Their coloration is quite variable ranging from dark brown to reddish brown, golden brown or olive brown and the hairs on the back are glossy tipped. Other characteristics used for identification include: 1) the tragus is blunt, 2) the third finger is longer than the fourth, 3) the hind paws have hairs that protrude beyond the toes, and 4) the calcar (cartilaginous extension of the ankle) is not keeled.

Each evening Leonard and I enjoy watching the bats in our yard emerge from their daytime hiding spots.

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One Response to Little Brown Myotis

  1. usermattw says:

    I’m trying to imagine eating half my body weight in food each night! 🙂

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