Two nights ago I went down to the newly cut field, the one I call “Field of Dreams” because it opens to the Northeastern sky allowing me to view the Great Bear, Cassiopeia and other constellations, meteor showers, as well as rising winter moons (my favorite). I sat down in the stillness listening to the crickets under a charcoaled sky. The rising moon was mostly hidden in the trees that rise over the southeast. Oh, it was so peaceful there with the sound of running brook water nearby. Newly mown hay wafted up embracing me in a cloud of scent.
Suddenly, to my great astonishment the sky was filled with bats. Bats? Maine has suffered a steep decline in some bats because of white nose syndrome. It had been years since I had seen so many. They dove around my head as my spirits soared. I noticed almost immediately that two sizes of bats were visible. And they kept on coming.
I left time behind me while gazing upwards. When I came to I realized that the bats were all appearing from the same direction. They must have a roosting place nearby, and I thought I might know just where…
I stayed watching the show until the sky grew dark. Last night I returned to the field at the same time wondering if I would see the bats again. This time I was rewarded by seeing bats emerge from the same direction after about a five – minute wait. The difference this time was that only the larger bats were visible. I was puzzled. Watching silhouettes against the sky made it impossible to determine the kind of bat or bats that I had seen but I guessed that one species was the Little Brown Bat and perhaps the other was the Big Brown Bat? I knew that females were larger than the males but this couldn’t account for the distinct difference in size between the two kinds I saw.
The Little Brown Bat is a species that is well known. They are very small with an overall body size that is from 2.5 inches to 4 inches. However, in flight their wingspan can stretch to eleven inches. They also weigh no more than half an ounce.
In contrast the Big Brown Bat has a body that is 4-5 inches in length, just the size of the larger bats I saw. Their wingspan is 11 to 13 inches. Surely I had seen both species that first night?
I already knew that these two kinds of bats roosted together during the winter months. Both species mate in late summer /fall. The Little Brown bat gives birth to one pup about two months later; while the Big Brown bat practices delayed implantation and doesn’t give birth until spring. Both bats have young that are totally dependent upon the mother for at least a month.
Both bats prefer areas with springs, swamps, brooks etc because there are so many insects available and my little marshy field provided the bats with a perfect environment.
Both bats have a large distribution throughout the United States so we have them here and in New Mexico. Weirdly, there are no Little Brown bats in either Texas or Florida. Pesticides?
The summer I stayed in Abiquiu I would wait until dusk and then go out while the cicadas (cactus dodgers) were screeching to watch the evening sky dance in the heat. The bats I saw in Abiquiu all seemed to be the same size. I guessed; Little Brown bats. However, even in the open spaces of the desert I never saw more than a few streaking through the dusk at one time.
Both species hibernate during the winter. Both bats like warm caves/mines (hibernacula) during colder months but during the summer they roost in hollow trees, rock outcroppings etc and even around/on houses.
Bats can consume up to half of their body weight each night and most captures occur during flight. Both have canines that are shaped in a way that allows them to hold onto their prey while flying. They will also use the tip of their wings to capture food. On occasions when food is scarce bats slow their heart rate to conserve energy while sleeping during the day.
To locate their prey, most insect-eating bats use echolocation. The bat emits a high frequency sound that bounces off objects in their environment. They can then determine the location and size of prey by listening to the sound echo that returns to them. Both bats are nocturnal and hunt most actively for a few hours after dusk. New mothers sometimes eat more than their own body weight in a single night. Eating insects plays an important role in the bats’ ecosystem (and ours!) by controlling bug populations near their roost sites. Prior to summer/fall mating Little Brown bats often appear in large swarms – if the size difference hadn’t been so obvious between the two bats I saw I would have assumed that a sky full of bats had to do with mating.
Once the young are born, they are dependent on their mother for food and warmth. At about one month of age, these bats can fly and catch insects on their own. Each mother has one pup a year and can identify her offspring based on scent and calls.
White nose syndrome has caused a steep decline in Little Brown bat populations. This devastating fungal disease affects hibernating bats and kills them. So far non – hibernating bats seem immune. Like so many diseases this one arrived from another continent. (Humans always seem to be the vector for the spread of diseases, and now we have Corona Virus that is killing us too). One source suggests that the Big Brown bat seems to be more resistant to this threat but I couldn’t find other support for this notion.
During hibernation bats can withstand a temperature change of nearly 120 degrees Fahrenheit without suffering any damage.
Pesticide build-up, deforestation, and mining are detrimental to all bats. These threats to bats should be taken seriously because we need bats to help control unwanted insect populations.
In the meantime I am going to continue to walk down to the field each night to see what might be happening with the bats, these curious mammals who have captured my imagination with their presence. I want to know just how long they will stay around.