Big Brown Bat censusing

Big Brown Bats roosting

photo from http://www.bu.edu/


Big Brown Bat in flight

photo from http://www.uwgb.edu/

White Memorial's Green Barn, which is located in the Main Area right behind the Museum, has hosted a Big Brown Bat colony for as long as anyone can remember. Since 1999, we have conducted sporadic censuses of this colony, usually as they exit in the evening to feed. This work has become increasingly important in the past few years with White Nose Syndrome decimating bat populations. Little Brown Bats are now greatly diminshed in numbers around this area because of this disease, but Big Brown Bats are still holding on in good numbers. They may not be affected by this disease quite as badly as other bats, or it is just a matter of time before it hits them hard, too. This year they had problems dealing with prolonged cold, wet weather in June. We found a total of 22 dead pups on the floor of the barn during this time period. Our censusing has also been adversely impacted by persistant lousy weather this year. Bats are not inclined to fly in the rain, so we don't try to census them under those conditions. With many other tasks to perform, it has been hard to find time on nice evenings to count the bats. On one such evening in early July I counted 193 bats exiting the barn. I didn't have another opportunity until Saturday, 8/6, when the bat census was supposed to be a major component of our "Serenade for the Bats" program for the public. However, heavy rain descended upon us about 5 minutes into the count after 70 bats had emerged. Not only did bats cease to come out, but the bats that had just come out went right back in. We quit counting them at that point. The rain didn't quit until the next day. I was a lot luckier the following Saturday, 8/13. The weather was mostly clear and warm with a light breeze. I parked myself on the northwest side of the barn where I could see the primary exit point under the peak of the roof on the west side and the secondary exit out through the front doors on the north side. I started watching for bats at 7:35 p.m., but didn't see the first one emerge until 7:47. The peak action occurred between 7:55 and 8:05. The last bat exited the building at 8:17. I went into the barn at 8:25 to see if any bats were still there, and didn't see any. The total that night was 164 bats, with all but 13 exiting from the west side. Almost all of them flew toward the Lake Trail and Ongley Field. The weather this past Saturday evening, 8/20, was also perfect for the bats and for us to count them. This time it was part of our "Things That Go Bump In The Night" program for the public. Twenty people participated in this walk which wound up at the Green Barn at 7:40 p.m. We postioned ourselves to see the west and north sides easily, and were rewarded with a total count of 149 bats between 7:45 and 8:20 p.m. Just like last week, the peak activity occurred around 8 p.m. When we went into the barn at 8:25 to check for remaining bats we didn't see any. All but 9 of the bats had exited from the west side of the building. We can't account for the decrease in bats with any certainty. We could have missed seeing bats exit the east or south sides of the building, or they may have been roosting in a different building, or they may have left the area, or they may have been eaten by an owl or other predator, or they may have died from some other cause. We did look for dead bodies in the barn and didn't see any. It is interesting to note that I saw a Great Horned Owl perched on the barn's roof right over the exit hole on Tuesday, 8/9, and we heard a Barred Owl hooting from the Interpretive Trail on Thursday, 8/11. We'll see what the rest of the summer brings for bat numbers as we continue to try to count them on a weekly basis. The more people helping to count, the better, so come on out.