Post-Volant Emergence Count of Bat Colony at the Green Barn

On July 25^th a second count of the bat colony in the Green Barn yielded a total of 167 Big Brown bats. The previous bat survey took place May 30^th when James Fischer and I counted 127 bats. The May count represents the number of bats before the pups begin to fly (pre-volant) and the July count represents the number of bats after the pups begin flying (post-volant). Therefore, the comparison of this data gives us reliable information about reproduction rate, as well as population growth. It is always a positive sign to see the number of bats increase, although we would have liked to have seen an even higher count, such as in 2010, when 286 bats were counted at the Green Barn. Since White Nose Syndrome is still spreading and devastating bat colonies, the data that is collected is critical in helping researchers measure the fallout of this disease and further explore other possible factors affecting bat population. We have observed that weather conditions greatly affect whether or not bats leave their roost at sunset. On July 18^th we attempted to do a post-volant count after a very hot and humid day with late afternoon thunderstorms. We were able to count only 105 bats emerging from the Green Barn and afterwards concluded that the data was inaccurate due to weather. In my opinion, bats will always be a unique and mystifying species. Their imperative role in our ecosystem should always be appreciated and we need to continue to protect these creatures as much as possible.


Two of Gerri Griswold's Big Brown bats.

Bat Maternity Colony Monitoring

A bat maternity colony monitoring project was held Wednesday, May 30^th at White Memorial. The survey’s purpose is to identify and evaluate the size of bat maternity roosts. This is achieved by conducting an emergence count of a specific roost before the pups begin to fly and an additional count after the pups begin to fly (sometime during the month of July). The emergence count started at 7:30 pm right before dusk, when the bats start to leave their den to feed. James Fischer and I, the surveyors, stood on either side of the barn and counted all of the bats that emerge.

The site that we decided would be most appropriate to monitor a bat colony is the two-story, open barn, known as the Green Barn, that holds White Memorial’s truck, van, and miscellaneous landscaping tools. There is a well-known roost of Big Brown bats (Eptesicus fuscus) that occupy the ceiling of the barn. From 7:30 to 9:09 pm we counted a total of 127 bats emerging from gaps at the top edge of the barn. Big Brown bats have black wings with a brown furry back and paler fur below. They are a very common bat in Connecticut, and typically are found in forests, but they can also live in crevices of buildings and caves.

Green Barn where bat survey took place.

Big Brown Bat
Photo by Jim White
http://02b93fb.netsolhost.com/

Opening from which most of the bats emerged.

It is important to document colony declines and losses to accurately track population change, especially to monitor the effects of White-Nose Syndrome, which since 2006, has killed over 5.7 million bats in Eastern North America. Bats play a crucial role in maintaining an ecosystem balance and consume thousands of mosquitoes and other insects every night.

This project is hosted by Connecticut DEEP Wildlife Division, who encourage volunteers to make counts wherever a bat colony is known to exist. Researching a wildlife disease is expensive, therefore more committed volunteers will help DEEP retain and use grant money to help combat this destructive disease.  

Bat Maternity Roost Microclimate Monitoring

(l to r) Ethan Toczko and Brian Blais (CT DEEP, Wildlife Division)
download data collected by datalogger.  

The datalogger is located in rafters of White Memorial's Green Barn
 and collects temperature and relative humidity reading periodically.  

Ethan Toczko and Brian Blais (CT DEEP, Wildlife Diversity Unit Technicians) downloaded some information that has been steadily collected for the past summer season.  Jenny Dickson (CT DEEP, Supervising Wildlife Biologist) is studying the microclimate of Big Brown Bat maternity roosts and associating this information with prevalence of White Nose Syndrome.  White Nose Syndrome (WNS) is an emerging infectious disease that kills bats primarily during the winter season while they are hibernating but has been observed in young animals who are dispersing from the roosts where they were born.  Recently, the disease causing agent was verified as a fungus that is native to Europe and brought to North America.  This invasive species has caused as much as 90% of the bats to die each year while hibernating in Connecticut's underground cave-like structures.  Fortunately, Big Brown Bats are the only hibernating bat species in CT not experiencing this level of mortality but some animals do die from WNS each year.  The datalogger is located in the rafters of White Memorial's Green Barn and collects temperature and relative humidity readings.  Although the data is collected continuously and culminates in thousands of data points, we only have to pull out our tallest extension ladder to download the data once a year!  Finally, technology that creates less work!

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.