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Wildlife Fact:

Indiana bats live an average of 5 to 9 years, but some have reached 14 years of age.

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Summer Bat Count

Got Bats? Help us keep tabs on NJ's bat population.


Image of A bat emerges from its summer roost site.A bat emerges from its summer roost site. © MacKenzie Hall

The Summer Bat Count was created in 2003 by the Conserve Wildlife Foundation and the state's Endangered and Nongame Species Program (ENSP) to gain a better understanding of how NJ's bats are distributed, what conditions they choose for roosting, and how their populations may be changing over time. This volunteer project relies on New Jersey residents to tell us where the bats are. So if you know of a place where bats roost in the summertime - like an attic, barn, bat house, church, or tree - then we'd love to hear from you!

Participating in the Bat Count

First, you have to know of a bat roost and be able to identify the bats' entry/exit points. Bats often find their way in and out of buildings through an opening in the eaves, a ridge vent into the attic, a gap in soffit boards where they join at the peak, or the space where the chimney meets the house's siding or eaves. Sometimes bats roost behind shutters or under roofing, too. Watch closely at dusk for their swooping silhouettes. You may even hear their mousey chatter as they get ready to depart.

We ask Summer Bat Counters to conduct four bat counts per summer - two between May 15 and June 21 (before pups can fly) and two more between July 6 and July 31 (when pups are flying and exiting the roost with their mothers). Making sure you do all four bat counts will allow us to best compare data from year to year and between sites. Let us know if you need help counting!

The bat counts are pretty simple:

  • Arrive at your bat roost by sunset time. Bats will begin to emerge 10-15 minutes later, at dusk.
  • The air temperature should be at least 55 degrees (F), no rain, and with wind speeds below 15 mph.
  • Sit or stand outside so that the bats' exit point is visible from a comfortable distance. More than one person might be needed if bats are exiting from multiple points.
  • Don't shine a flashlight at the exit point - bats are shy and cautious and might not come out.
  • Tally the bats as they fly out for their nightly insect-eating! Most will have left by the time it's totally dark outside. Record your observations on the data sheet.
  • Mail us your data sheet at the end of the summer.
  • Do not enter bat roosts or handle the animals.
  • Please respect private property. Ask permission if the bat roost is on someone else's land.

If you know of a summer bat roost and would like to participate, please contact us or simply print and complete a Summer Bat Count data sheet.

Recent Trends

Since White-nose Syndrome (WNS) hit New Jersey in January 2009, Summer Bat Count information is even more critical, helping biologists to measure the fallout of this devastating disease. During the first summer post-WNS (2009), summer "house bat" roosts dropped an average 31% in size. We quickly realized that colonies of little brown bats were much more impacted than colonies of big brown bats.

In the 2010 Summer Bat Count, we set out to better measure those differences. The results were staggering: while overall colony sizes had dropped now by a total 41% compared to pre-WNS counts, the little brown bats had dropped by 80% while big brown bats had actually increased by 41% in our sample.

In the summer of 2011, our Summer Bat Count sample showed an 86% decrease in little brown bats and a 31% increase in big brown bats since pre-WNS counts. Are big browns taking advantage of newly available roosts and a glut of insects? When homeowners are willing, we are now giving out bat houses to install near existing big brown bat colonies in hopes that they will expand and help replace the bats that have been lost.

By the end of 2012, we had given out or installed more than 30 bat houses to help existing bat colonies grow and to provide alternative roost spaces for bats that were being evicted from buildings. We'll monitor these new structures to see how successful they are. It's an effort we could easily expand. In the meantime, we received data from 30 roost sites in 2012, tallied 1,502 unique bats, had 17 new roosts reported, and had representation from every NJ county except Gloucester, Hudson, Middlesex, and Union. Overall, big brown bats are stilll ~27% more abundant than our pre-White-nose Syndrome numbers showed, while little brown bats have leveled off at a ~80% reduced population (in our small summer sample).

Image of Annual Summer Bat Count totals, from baseline (pre-WNS) to 2013, corrected for sample size (n=22 sites). For more details, see our 2013 Summer Bat Count Report below.Annual Summer Bat Count totals, from baseline (pre-WNS) to 2013, corrected for sample size (n=22 sites). For more details, see our 2013 Summer Bat Count Report below.
Learn More:
  • Want to know more about your "house bats" or find out how to solve a bat problem? Visit our Bats in Buildings page.
Download 2014 Summer Bat Count Data Sheet

2014 Summer Bat Count Data Sheet - 64.1KB
Please complete 4 emergence counts and record your bat colony info on this form.

Download 2013 Summer Bat Count Report

2013 Summer Bat Count Report - 278.8KB
Little brown bats continue to drop; big browns come out on top.

Download 2010 Summer Bat Count Report

2010 Summer Bat Count Report - 151.3KB
Mixed results from the 2010 count; White-Nose Syndrome research continues.

Download 2009 Summer Bat Count Report

2009 Summer Bat Count Report - 138.4KB
CWF's report on bat counts and white nose syndrome.


Contact Us:

MacKenzie Hall, Private Lands Biologist: Email
908.782.4614, Ext. 104


Find Related Info: Bats

Adopt an Indiana bat!

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Adopt an Indiana bat and help Conserve Widlife Foundation protect this endangered species in New Jersey.

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Help Protect NJ's Bats!

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Over the past two years White Nose Syndrome has reduced the population by 80%. Your donation can help us protect bats in New Jersey.

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