Beyond Human: Bat’s Night Vision

Contrary to the saying “blind as a bat,” bats can see just as well as humans in the daylight. However, in darkness bats have a far superior ability to see, and are able to hunt their prey using a sense that is not shared with humans, a sixth sense.

“Bats are interesting I think from two perspectives,” said Dan Bachen, Senior Zoologist at the Montana Natural Heritage Program. “One, they are the only group of mammals to have true flight. There are some rodents that glide, but bats are capable of propelling themselves through the air and flapping their wings. The other is that they echolocate.”

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Bats listen for the echoes produced by their ultrasonic calls (sounds that are above human hearing) to detect objects around them. Echolocation allows bats to navigate using reflective sound just as effectively as humans are able to navigate using their eyes in daylight. A bat’s brain allows it to see in echolocation, giving it continuous “pictures” of the world around it. Consider the imagery of a strobe light. With a strobe light, humans only see the world when the strobe light flashes. When bats fly through the night giving out ultrasonic calls, they interpret each call as a short pulse. However, if they need to see more, they can generate a faster rate of calls. As with a strobe light, the faster the pulse, the more the information is perceived as a continuous picture.

A bat’s routine call rate is 5 to 10 calls per second, but as it gets closer to its prey it increases its rate of calls, and briefly reaches 200 calls per second before it strikes. It takes a lot of energy to emit these calls.

Scientists study bats by collecting data on these calls. In Montana, the largest bat echolocation acoustic collection program is currently in progress. Through acoustic stations scientists have been able to monitor bats over time and have expanded the habitat range of certain bat species as well as significantly expanded the number of bat species present in Montana. “So it’s been amazing, just the ability to not only see where a species is on a given day but to see where these species are over an entire year,” said Bachen. “What we are primarily interested in is getting the information prior to white nose hitting.   Say 10, 20 years ago we had a pretty good idea of what species lived here and their general habitats, but we did not have a lot of good data on what the populations were like, what areas are actually occupied, and the amount of activity at certain sites. Those are good things to know and if for no other reason, just being able to assess whether white nose is affecting our bats or not.”

White nose, a fungal infection affecting bats, had been contained to the east coast for some time. It was detected in Washington state this summer, potentially pushing up the date when the fungus might be spread to caves in Montana. “I think the bottom line is, through proactively getting out there and getting that data, we are in a good position to be able to assess the affects of white nose. Also, if a treatment is developed, we will be able to make more informed decisions. Currently, there is no other way to manage white nose except for decontaminating your gear before you go into caves, making sure that the fungus isn’t spread by people,” said Bachen.

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