An online resource based on the award-winning nature guide –

Female Big Brown Bats Forming Maternity Roosts

5-7-15  big brown bat 022Big Brown Bats have emerged from hibernation and have been active for several weeks. It is in the spring that a female Big Brown Bat becomes fertilized with sperm she has stored in her uterus over the winter. Reproductive female Big Brown Bats collectively form a maternity roost at this time of year and each bat typically gives birth to a single pup in June, after about a 60-day gestation period.

While both Little and Big Brown Bats were affected by the fungus causing White Nose Syndrome, the Big Brown Bat population has not been decimated like the Little Brown Bat population. In some locations, Big Brown Bats have even thrived, taking over summer roosting spots formerly occupied by Little Brown Bats.

Naturally Curious is supported by donations. If you choose to contribute, you may go to and click on the yellow “donate” button.

8 responses

  1. Connie Snyderr

    Can they see with those big eyes? I always heard that bats are blind.

    May 21, 2015 at 8:20 am

    • Hi Connie,
      According to the Director of the Organization for Bat Conservation, bats can see three times as well as humans! (Plus they use echolocation.)

      May 21, 2015 at 10:20 am

  2. Fascinating! How big is a big brown bat compared to a little one? I would like to be able to identify which kinds I’m seeing here and on the Cape, at a distance. In Sunapee we’ve noticed fewer and fewer bats each year, just like the birds.

    May 21, 2015 at 8:55 am

    • Hi Susan,
      Here’s what one bat person has to say about telling a Big Brown from a Little Brown bat. Hope it helps!

      The physical differences between Little Brown and Big Brown bats are subtle. Even with one in each hand it is still difficult to tell them apart. I have studied both species for many years, I have taken thousands of photos and I have also studied them in person every chance I got. Only now am I confident enough to say that I can tell them apart.

      The most obvious physical difference between Big Browns and Little Browns is the nose.

      Little Brown Bat: The nose of the Little Brown bat is short and almost entirely covered with fur. It also looks “smooshed” and is very short.

      Big Brown Bat – The nose of the Big Brown bat is generally longer than that of the little brown bat. The space from the ear-lobe to the tip of the nose is almost fur-less.

      Large Big Brown bat
      Generally speaking, size is not a good way to tell one species from another. There are just too many variables that go into the size of a bat (age being the most significant). If you had one bat of each species that were both the same age the Big Brown bat would be significantly larger. I have found that the wingspan of adult Big Brown bats is between 11-13 inches. Adult Little Browns on the other hand have a wingspan of 6-9 inches.

      May 21, 2015 at 10:27 am

  3. Kathie Fiveash

    I see hardly any bats anymore – maybe because I’m accustomed to being on the island in bat season, and we don’t have many out there. But I remember the sky full of bats when I was a child in Vermont, I’m thinking that there must always have been many more little brown than big brown bats, and that the white nose syndrome has vastly reduced the total number of active bats. Is this true? Do we know what percentage survive the fungus? Are there genetically resistant individuals that can rebuild the population? I’ve read that we can expect many more mosquitoes now that the bats are so few. Not to mention the wonder of watching them zigzag across the sky at dusk.

    May 21, 2015 at 12:51 pm

  4. Huge thanks for conveying some good news about bats in New England. “My’ Little Brown Bats are back, much to my surprise and delight.

    May 21, 2015 at 3:27 pm

  5. I love bats! Glad to hear that fungus hasn’t been as destructive to the Big Browns. A small ray of hope.

    May 24, 2015 at 9:18 pm

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s