Guano pile quick check

Participants – Bill Gee
Rita Worden
Seth Colston

Time in – 8:00am, Time out 11:00am

For many years we have assumed that Carroll Cave was a summer host to a maternity colony of grey bats. The bats use several guano piles located in Carroll Passage upstream from the Lunch Room. We have done trips through there in October for about 15 years. The guano gauges always show signs of use at sometime in the previous year. We have never had any more accurate idea of when the bats are roosting over the guano piles.

In March 2021 a trip went through the area on the way to the Mountain Room. In March we saw no signs of use on the guano piles. A survey team went through in early May. They reported no sign of either bats or usage on the guano piles. If maternity colonies are using the cave, they should be there from about early April through mid to end of August.

The facts did not agree with our assumptions, so we decided to run a very quick trip to the guano piles t see what is going on. Since there were two other trips going this same weekend, we tacked a third trip on for Monday.

To help out with the survey, we were loaned a thermal infrared camera by Vona Kuczynska of the U.S. Fish and Wildlife Service. Seth stopped by Vona’s house on the way to Carroll Cave Saturday afternoon to pick up the camera. In addition I took along a laser thermometer so we could check ceiling and wall temperatures.

Rita, Seth and I all camped overnight at the silo. We were all on a trip the day before. Since there was only three of us, we were able to get in the cave earlier than usual. Everyone was geared up and down the shaft by 8:10am.

The trip through the Water Barrier to the first set of guano piles took a bit less than an hour. We were all wearing red lights which we turned on as we approached the area. Seth got out the thermal camera and checked the ceiling. There were no bats at all.

Guano gauge number one showed some use. Gauges two and three were blank. We saw a couple of fish and one larval salamander in the stream. The ceiling temperatures ranged from 55.7F to 56.2F.

Moving on to the next set of gauges, we again saw no bats. Guage 4a showed some use but 4b was completely clean. Gauge 5 had one turd on it.

Guano gauge 6 was about 25% covered. About 4 foot diameter area of fresh guano. The gauge is on the edge of the fresh guano area. The fresh guano had a lot of small insects like gnats on it.

Guages 7 and 8 were clean. I checked ceiling temperature here and found 56.5F to 56.8F. I took readings on both ceiling and wall, and there was no appreciable difference.

At guano gauges 12a and 12b, the ceiling temperatures 55.3F to 55.9F across several readings. These two gauges had a lot of fresh guano. There were no bats. Seth took some photos with the thermal camera. The fresh guano showed up clearly as warmer than the surroundings. The laser thermometer got readings around 56.5F to 57F on the guano.

Guano guages 13 through 15 were paydirt. We heard the bats chittering while we were 30 or 40 feet away. We switched over to red lights. and moved to within about 20 feet. Seth took several photos and a couple of movies with the thermal camera. We did not get close enough to piles 14 and 15 to see their state. Pile 13 had nothing.

I estimated the area of bats at 10 to 12 square feet. Rita estimated half that, and Seth estimated about 8 or 9 square feet. It is hard to get a good look with just red lights.

I took some temperature readings with the laser thermometer. The bare ceiling and walls were around 56F. Temperature in the middle of the cluster was 72F.

There was an odor but it was not strong.

We were there for about 5 minutes, then we around turned and left. We did not turn on our white lights until we were several hundred feet away. Even so, for the next 10 minutes of moving through the cave there were three or four bats flying around us.

The trip back to the ladder was just as quick as the trip out. We were at the ladder by about 10:40 and all out of the cave by 11:00am.

After changing and having lunch, we gathered in my camper to review the photos from the thermal camera. I downloaded them to my laptop for viewing. I also downloaded photos of the guano guages, then copied all photos and movies to a USB stick drive. Seth will pass them on to Vona when he returns the thermal camera.

We packed up and left. Everyone on the road by 2:00pm.

Guano gauges

1 = 50% coverage, 2 or 3mm depth. Lots of fuzzy fungus. Also fungus on the pile around it. Almost no odor.
2 = Sprinkling 10%, 1mm. No fungus.
3 = Completely clean. Shelves above the pile also had nothing new.
4a = One or two turds.
4b = 65% 2 or 3mm, lots of fuzzy fungus.
5 = one turd
6 = 25%, 2mm. Fuzzy fungus growing on it.
7 = Clean
8 = Clean
9 =
10 =
11 = one turd
12a = 95% 4mm. Fungus everywhere except on the top of the pile. Strong odor.
12b = 90% 5mm. No fungus on the gauge but plenty on the pile. New guano was the top half of the
13 = A few turds.
14a = No data
14b = No data
15a = No data – Bat cluster was over pile 15.
15b = No data

Bill Gee