More Batty than Usual

11 October 2007 El Malpais NM, New Mexico -- Tres mas cuevas

This is a maternity/nursery roost of Mexican free-tailed bats (Tadarida brasiliensis). You can actually see the "free-tails" on several of the flying individuals in this image! I estimated this roost around 3000 individuals. I was surprised to see so many bats so late in the season. I had specifically chosen to conduct biological inventories in early to late fall to avoid disturbing bat maternity and nursery colonies. Fortunately, all the pups associated with this colony are now vagile (they can fly), so our presence does not place the pups at risk of being knocked off the ceiling.

We have three caves on today’s agenda. We will conduct time constrained searches and pull traps at Dipulran Den and Dead Snake Caves. Once this was completed, we were going to Guano Grotto Cave to deploy traps.

As I mentioned in a previous blog, Dipulran Den and Dead Snake Caves are heavily used by tourists. They are also characterized as ice caves. Thus, I did not anticipate finding much in these caves. In Dipluran Den we collected only one cricket. Fortunately for us, it was a male and we could use this specimen for identification. However, we did encounter one big brown bat and at least five hibernating Townsend's big eared bats roosting within the cave.

Big Brown Bat (Eptesicus fuscus) in a torpor within the twilight zone of Dipluran Den Cave.

This Townsend's Big Eared Bat (Corynorhinus townsendii) is most likely setting into hibernation for the winter. During the cave detection research, I've counted upwards of ~100 hibernating Townsend's bats within the dark zone of Dipluran Den Cave.

We did not encounter one arthropod in Dead Snake Cave.

Once we were done with these two caves, it was time to enter the Guano Grotto. This cave was another world. This cave is aptly named. The guano is so extensive that we had to wear respirators while working in this cave. Respirators are required to protect us from histoplasmosis . This is caused by a fungus that can enter the lungs and grows on the alveoli as polyps. In most cases, this condition is not fatal, but if you get it, you may wish it was.

Over 90 % of this cave was covered in a thick carpet of bat guano. As we walked through this cave, the floor felt as if we were walking on a padded floor. The walls were covered in guano and in some places there were actually stalactites of guano. Pete believes there is mycelium (a type of fungus) binding the guano and decomposing material together. This is probably how the guano was forming stalactites on the walls.

As we were pulling tape to mark our stations and getting deeper into the cave, I heard bats. Once I rounded a bend in the passage, I realized there were a significant number of Mexican free-tailed bats (Tadarida brasiliensis) still in residence. I estimate the colony at approximately 3000 bats.

Image: Ara and Pete pulling tape to establish our sampling stations. Pete is featured in the image.

The nutrient loading due to the presence of these bats and the deposition of guano has resulted in one of, if not the, most biodiverse cave on the monument. We collected numerous spiders species, Rhadine beetles, Eleodes beetles, crickets and fungus gnats. I expect we will find numerous additional species through the trapping effort. We will learn of our success when we pull the traps on Sunday.