Winter Guests in the Chiroptorium

Which species of bats are still here in February?

It is generally assumed that most Mexican Free-tails (Tadarida braziliensis) head for Mexico and other countries south where the temperatures are warm and bugs are available during the cooler months between October and March. However, it is clear from the pictures I've taken of the bat boxes inside the Chiroptorium that many bats have stayed in the bat-boxes where the heat of their bodies accumulates and they stay warm. We think that in the warm spells they fly out in the evening and find some insects to eat.

In "Bats of Texas" by David J. Schmidly indicates that Cave Myotis (Myotis velifer) spend winters in caves, rock crevices, old buildings, culverts, and bat houses in central and north-central parts of Texas. The two inhabited bat boxes in the Chiroptorium have populations that consist of both species. In the photo below the 2 bats that are in sharp focus are Cave Myotis. Their fur is tan and their ears and fur around their nose and eyes is dark.

Most of the bats seen clearly are Cave Myotis. This box is in the small dome.

The photograph below was taken of the box in the large main dome on the 8th of Feburary. I sent it to several bat biologists, and the answers I got on which species can be identified in the photo is that both Mexican Free-tails and Cave Myotis are sharing this box. Another biologist thought that all of the bats looked like Free-tailed bats in this picture.

Most of the bats in this box in the main dome are Mexican Free-tailed bats.

What else do we find in the Chiroptorium?

On the cave floor there are many bat skeletons. Here we have 2 skulls, a spinal column with ribs, and a hand-wing.

Dermestid beetles live on the floor of caves with bat colonies. They are flesh eating and so are their larvae.

Dermestid beetle larvae exoskeletons are found on the floor around bones in winter. They possess projections which look "furry". They are meat-eaters, and keep the cave floor clean of the flesh of dead bats during warm months.

Some scientists study guano (bat droppings). Justin is collecting guano to send to a professor who looks for insects, eggs, and tiny creatures.

What can we do to increase warm habitat for bats in winter?

When Dr. Thomas Kunz from Boston University visited the Chiroptorium in early January he and the other bat biologists were amazed to see that there were lots of bats in the bat boxes. They suggested that if we have more bat boxes we could have more bats stay during the winter. So, Steven and Justin built 3 more bat boxes, to be hung on eye-hooks embedded in the gunite on the ceiling which were placed there in 1997 when the Chiroptorium was built. The builder and designer, Jim Smith, thought that we might want to add items in the future. We thank him for that, and for his thoughtful design, construction and additions.

To install them, Steven got the box up on the shorter ladder, Justin climbed up to the ceiling on one side and got it firmly hung, then moved the long ladder to the other side and hung that side to the hook.

First the box is raised.

Steven, 6'8" tall, holds it up for Justin to hang the right side.

Then Justin moves his ladder to the other side and hangs the left side.

The large dome of the Chiroptorium now has 4 boxes around the second curtain and a box in the center.

We hope and expect that our population of females (along with a few males) will return to the Chiroptorium in March. I will continue writing about them as spring arrives and bats return. Let me know if you like hearing about bats.

Crazy About Bats!

Bats, the Chiroptorium, and bat researchers.

The Chiroptorium is our man-made bat cave. Chiroptera is the order for bats in the family of Mammals, which is the origin for the first part of the name Chiroptorium. The second part of the name "torium" comes from the end of auditorium which is a large place for a gathering. So, Chiroptorium is a large place for bats to gather. In March each spring, Mexican Free-tailed Bats (Tadarida brasiliensis) arrive in large numbers from their winter homes in Mexico, Central and South America. Because our cave is a nursery colony, most of the bats are pregnant females. They leave each evening as the sun sets to find food, which is lots of flying insects, especially moths.

In the middle of June one baby is born to each mother bat. The babies, naked, pink and flightless, are deposited in a contiguous area on the ceiling or wall of their cave. The heat generated by all the close bat-bodies (up to 400 per square foot) help to keep them warm. Mothers leave their babies in the cave when out hunting for food at night. Each mom relocates her baby by calling to her pup when she returns. As she gets close she can also smell her offspring. Her milk is rich and high in fat, and her baby grows quickly, and within a month the pups are nearly as big as an adult, furred and ready to fly and feed on their own.

Dr. Gary McCracken on the left in the above photo, has done a lot of research in Texas, which has increased our understanding about Mexican Free-tailed bats, how they live, what they eat, and how important they are to agriculture. Using weather balloons with echolocation sensors on them, he was able to find out that free-tailed bats find and fly into clouds of migrating moths that they love to eat, and which provide them with important nutrition. These moths lay their eggs on corn, cotton and other crops, and the caterpillars eat the developing plants. Therefore having bats eat lots of moths before they have a chance to lay their eggs is beneficial to farmers.

The huge colonies of Mexican Free-tailed bats in Central Texas live mostly in caves, but are also found under bridges like the Congress Avenue Bridge in Austin, and in culverts. When an continuous stream of bats emerge in the evenings for many minutes, and even hours, it is hard to imagine how many bats are flying in front of you. Until the last few years there was no way to accurately count the numbers, until Dr. Tom Kunz, from Boston University, on the right in the picture above, developed a method using infrared video photography and computers. A continual infrared image of the bats emerging from the mouth of a cave, in which the warm bodies of the bats appear like little white dots moving against a dark background is read by a computer and the total number calculated.

One of Dr. Kunz's post-doctoral students, Dr. Nickolay Hristov, shown with his new Belgium sheep-dog three month old puppy, Coda, and another graduate student, seen below, Louise Allen came to The Bamberger Ranch in 2004 and conducted a count. The next spring they started a regular once a month count of our bats during the time the bats are in Texas. I remember the early counts were below 10,000 bats. However, we were thrilled when we realized that there were babies in the cave, which meant that even though the numbers were small, we had a nursery colony. Each year since then the numbers have increased dramatically and this year after the babies were flying the number reached 121,000.

Louise Allen-Hristova, who is now married to Nick, had also been researching the effects of stress on the growth of young bats. She has finished collecting information for her dissertation, and is now writing it. She will be awarded her Ph.D. soon.

Another doctoral graduate students of Dr. Kunz that has worked on our counts is Jon Reichard, seen above with his wife Jen who is an 8th grade science teacher. That's J. David Bamberger smiling on the right.

The research by Dr. Kunz's team has included counts on many of the Central Texas caves as well as Carlsbad Cave in New Mexico. This has added an important chapter to our knowledge of bats. We certainly thank them for their work here at Bamberger Ranch Preserve, and for their friendship.

Bat Conservation International (BCI), whose headquarters are in Austin, has a great deal of information about bats in Texas that is available to the public, both on line and in books that are for sale from their bookstore, which is also on line. In the months when there are nightly emergences from the Congress Avenue Bridge over Lady Bird Lake, there are specialists from BCI there to tell you about the lives of bats and how important they are to humans. It is a wonderful show, and I recommend that you get out and see it.