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Friday, June 17, 2011

Mist netting for bats!!! PART II

Tanner DeWolf erects bat mist net
(6/11, Canandaigua NY)
Our second night of mist netting for bats was as exciting as our first (see previous post). Again, the nets were placed in the woodlot along the main pathway. This provided a clear area for the nets themselves with a canopy overhead. Apparently, this is an ideal situation to capture many bat species. I know from mist netting birds that a net placed in the open is often spotted and avoided. I could only imagine that the canopy cover provided a barricade of sorts funneling the bats into the nets rather than around them. As I mentioned in my last post, we used three nets stacked on top of each other. This requires some very tall and light poles. Micheal and Tanner had a rig that consisted of four aluminum poles that fit together via tapered ends. At the top of the end pole was a pulley so the net could be raised and lowered like a flagpole. At the bottom of the first pole was a cleat to wrap the pull rope around. Each net also had two guide lines from the top that got tied off at angles to help secure the pole.

Even more interesting than the pole was the rig used to attach the nets. As you may have seen in my posts regarding mist netting birds, the elastic loops of the net are simply wrapped around the pole and if I need to lower the net, I simply tug on it until it slides down. However I am not stacking three nets on top of each other (the top of the highest net rises to about 25 feet off the ground). For the bat nets, a simple but ingenious series of PVC pipe slices and carabiners  is used to attach the nets. These PVC cookies are attached to a rope that can raise and lower the series. It worked very well and kept the nets properly spaced to boot.
Tanner assists John Van Niel in attaching mist nets
(Photo by: Elaina Burns)
As with the first night, we set the nets at sunset and noted the time. We were to check the nets every ten minutes. On the very first net check, we watched a bat actually fly right into the net. And to our surprise and delight found it was a red bat! First off, this was a new species for us. Secondly, it was really striking. That reddish color was amazing. Finally, Micheal had told us that we were far more likely to catch "cave bats" rather than "tree bats" as the tree bats tended to fly higher, above the tree canopy. And the red bat is one of the three species of tree bats in NY State. Tree bats roost singly, often under the bark of trees while cave bats roost colonially, often in caves. But common names can be deceiving. If I found a group of little brown bats roosting in a hollow tree, they would still be cave bats :)

Removing red bat from mist net
(6/11, Canandaigua NY)
Here is a photo of Clinton Krager taking the bat out of the net. Notice the sharp fold at the tip of the wing on this species. At first, I assumed the wing was damaged! But that is normal for this species. That fold is literally the last joint of a finger bone. Bats are in the Order Chiroptera which translates to "hand wing" and that is a good description of their anatomy. The bones you see that form the support for the wing membrane are finger bones. Note that the thumb has remained small and usually has a sharp nail to aid in climbing. By the way, most of the bats we removed from the nets squawked and showed their teeth. This bat was not in pain but clearly he was not happy.

Dorsal side of a red bat showing the furred tail
and wing membrane
(6/11, Canandaigua NY)
We brought the bat to Micheal to confirm the identification and he showed us a few other key characteristics of tree bats. He had mentioned that they were hairier than the cave bats during our Friday lecture, but I wasn't sure what he meant. Here he shows us the fully furred rear of the tail as well as the partially furred back of the wing. I wonder if these are adaptations to retain heat for a species that roosts alone rather than in a group.

Measuring the forearm of a red bat
(6/11, Canandaigua NY)
There are some standard measurements taken on all bat species. In the last entry, I talked about measuring the tragus (inside the ear). Here is a photo of Micheal measuring the forearm of the red bat. He told us that it is standard to take all measurements on the right side of the animal and that forearm measurements are unique to bats. There would be little use in taking that metric in other types of mammals.

Inspecting the nipple of a red bat
(6/11, Canandaigua NY)

While taking measurements, Micheal determined that this bat was pregnant. He pointed out the somewhat obvious bulge and remarked that the weight of the pup (or two in some species) is a considerable load for the mother and impacts her ability to fly and specifically on her ability to take off. Micheal gently blew on the hairs of the bat (much as I do on the feathers of a bird when I look for a brood patch) in order to expose the nipples. Since her nipples were hairless, that indicated that she had been a successful breeder in the past. Apparently, once a pup nurses, the hairs on the nipple are worn off and are never replaced. It is not possible to tell how long ago she had young or how many of them she produced. But it is a good measurement that shows she HAS been successful in the past. I am willing to bet that most people have never thought of bat milk before! :)

1 comment:

  1. Good stuff, JVN.

    Looks like a ton of fun!

    I've done alot of Anabat work in the past, but have NEVER done mist-netting, much to my dismay.

    Maybe some day!

    Looking forward to future posts.....


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