Friday, August 28, 2015

Bat Banding

 Last night was the last night of the Nevada BatBlitz, a weeklong event held annually at different locations around the state. (I wrote about the 2014 one here.) This year it was held in and near Great Basin National Park, and I participated two nights. This night we headed to Rose Guano Cave in the beautiful evening sunlight, scrambling up the rock with a bunch of gear.

This old sign soon will be updated, as recent studies have found that millions of bats use this cave for a night or two as they fly south in late summer. Where do they spend the summer? Hmmm, well north of Rose Guano Cave probably, but only a few locations have been identified, and certainly not enough for millions of bats. Lots of other questions remain about their migration routes (they don't use Rose Guano Cave on their way north in the spring, so where do they go?) and wintering and summering grounds.

Nearby is a beautiful arch. Sometime I'll have to explore it more.

The views into Spring Valley are great. In the distance is a wind farm, Nevada's only wind farm. Wind farms cause a lot of bat mortalities due to the pressure difference as the blades go around. A bat doesn't have to be struck by a blade to die, but the barotrauma (pressure difference) can cause their lungs to burst. Fortunately, the wind farm has tried to reduce bat mortality by turning off the blades when large numbers of bats come out of the cave.

You can smell the cave before you get to it due to the massive amounts of guano in it. That guano attracted attention and a mining claim was filed on it. An adit was built into the guano chamber in 1926, and early miners sold the guano as fertilizer and possibly to make explosives. Guano is high in phosphates and nitrates. The note on the wall below says: Danger Positively No Trespassing Rose Guano Mining Claim.

Located near that wall is this pole with sensors on it. A pole on the other side of the cave entrance looks similar. These sensors send a beam across, and when it is broken, that beam break is counted. There are two arrays on one side so bat egress (exit) and ingress (entrance) can be counted. The data is transmitted real time to the wind farm, so they know when to turn the wind turbines off. These sensors have helped biologists understand a lot more about bat use of the cave.

As some folks were setting up the gear to trap the bats, I ventured into the cave entrance a bit, the first time I've ever done that. We could see a deep pit below us that went down into the dark. The bats go further back into the cave. The smell of the guano was so strong that after a few minutes I was feeling a little queasy, and we weren't even next to the guano! It's amazing that the bats can withstand such high levels of ammonia.

Because so many bats fly out of this cave, only a single trap is used, called a harp trap. Fishing line is strung vertically, and when the bats encounter it, they slide down into the canvas bag at the bottom.

Here's a view of the cave entrance from inside. Before long the bats would start flying and darkness would descend.

Putting some high-tech finishes on the harp trap--pool noodles, to help the bats from getting injured.

Once everything was set up, we just had to wait for the bats to start flying. Folks from Nevada Department of Wildlife (NDOW), BLM, Great Basin National Park, Nevada Natural Heritage Program, Death Valley National Park, and Lake Mead National Recreation Area were helping.

Before long the bats started exiting. One comes out first, circles around, and reports back to the others. Then just a few stream out at a time, and then it can be hundreds per minute. They generally head south, towards the agricultural fields, where they will eat their weight in insects every night. Some will return to the cave for another night, others continue their trip south.

As they fell in the harp trap, those with rabies shots picked them up and determined gender, age (adult/juvenile), tooth wear, and reproductive status. A small metal band was attached to the arm.

Here is one of the banding stations.

It took about a minute or two to process each bat, then it was released.

We banded about 250 bats in less than two hours. This brings the total that NDOW has banded this summer up to 5,000! Wow. Hopefully the bands will help researchers learn lots more about where these bats spend their lives.

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