The chiroptorium is the artificial bat cave constructed by the Bambergers to try to bring a substantial bat population to the ranch. Like many others, I've photographed it from outside, but all that really shows is the big, artificial cave mouth. I haven't seen any photos of the interior since it was under construction (it was a work of art before its surface was covered with concrete and the whole structure buried). So, I've thought for a while that a spherical panorama ought to be shot inside it in order to clearly show people the end-result of that construction. However, the chiroptorium's success, in the form of the 120,000 Mexican free-tail bats that occupied it this year, kept me from entering to shoot a panorama before last Tuesday, December 4th, because we didn't want to risk disturbing the bats. With the arrival of winter the free-tails have returned to Mexico, so the chiroptorium's only residents are many hundreds of cave myotis tucked-away in the warmth of a pair of internal bat boxes, and untold legions of flesh-eating dermestid beetles occupying the foot or more of accumulated bat guano that covers the cave floors wall-to-wall. The consensus was that I could enter without disturbing the myotis, provided that I wasn't disturbed by the flesh-eating beetles. A pair of rubber boots proved to be adequate for keeping the beetles at bay, and the shoot went smoothly, to the continuous accompaniment of the chattering myotis.
The result is the following high dynamic-range, high-resolution QuickTime VR panorama. The panorama is 8.4 MB, so it may take some time to load.
The panorama initially looks from the main chamber into the exit tunnel. If you were an exiting bat, that's where you'd be headed. The tunnel to the right of that leads to the smaller second chamber, which leads in-turn to the very small, inner-most third chamber. The main chamber shown here is the best exemplar of the chiroptorium's design. Key features include the following:
- The chiroptorium was designed as sequence of intersecting domes. The domes were formed from an elaborate weave of rebar, which was then covered with metal mesh. Concrete thickened with fiberglass was sprayed onto the mesh (without that thickener, the concrete went right through the mesh). The richly textured interior surface created by that concrete is a design feature - it provides innumerable footholds for the bats. When construction was complete, the chiroptorium, built at the bottom of a small valley, was covered with earth, thus effectively filling-in much of the valley, and transforming the domes into a cave. (A large drain pipe prevents the remaining portion of the valley from forming a lake behind the cave, and keeps the cave floor dry.)
- The floor is covered with years of accumulated bat guano, which, when I encountered it, was a dry, almost fluffy layer of material, that must have been somewhere around a foot deep over the entire area of the floor. It is home to (among other things) a large population of flesh-eating dermestid beetles, which eat fallen bats. (Some of the white specks visible on the surface of the guano are bones. Some of the black, shiny specks are the beetles.) The invertebrate population of the chiroptorium is being studied by researchers who are interested in learning how the invertebrate populations typically found in bat-occupied caves establish themselves. Since the chiroptorium began as a clean slate, so to speak, the chiroptorium probably represents a unique opportunity for such studies.
- The ceiling of the dome is interrupted by three concentric vertical rings of concrete. They provide additional surface area on which bats may roost.
- Two bat boxes, one square and one rectangular, hang from the ceiling. They were a part of the chiroptorium from the beginning. Their purpose was to provide roosts for the initial population of bats. Their compactness is a feature with a small population: tightly packed into those boxes, the bats keep each other warm. At the time this panorama was shot, both boxes were filled with cave myotis bats, which find the boxes to be ideal winter roosts.
- The large tubes extending up through the ceiling are ventilation shafts, though they are not used while bats are present.
- The wood set into the wall covers the viewing gallery's windows. Those windows turned-out to be the reason that the chiroptorium went for years without acquiring a population of bats. I've heard conflicting explanations of why the windows were a problem for the bats, but, whatever the reason, once the windows were covered, the bats found the chiroptorium (now minus its "torium"-ness) a very agreeable home.
Margaret Bamberger supplies some details on the conflicting explanations regarding the windows: "Either/or or both are true (probably): (1) When flying around in daylight bats use eyesight for navigation. If light came through the window from the other side, it would look like an opening, and they'd fly into it. (2) Glass doesn't send back a signal to the bat's echolocation, because it has no surface variation, and the bats don't know that it is there. Bats will swoop down and try to drink from very flat surfaces that are horizontal. They have no experience with such surfaces on a vertical plane, except where humans put them. In a cave built for them it becomes a huge problem."
(I first met David Bamberger at a Bat Conservation International (BCI) outing to Bracken Cave, whose purchase he had years earlier organized on behalf of BCI. Having seen an article about the construction of the chiroptorium in the BCI newsletter years before, I asked him how the project had turned-out. He paused, then said unhappily "let me put it this way: I'm currently housing bats at five thousand dollars a head." During that period, I gather the chiroptorium was labelled by some as "Bamberger's Folly." It took years to realize that the observation gallery windows were the problem, but as soon as the windows were covered, the bats came, stayed, and bred, making the chiroptorium a bigger success with each passing year.)
Margaret Bamberger can say a great deal more about every aspect of the chiroptorium, and what they've learned from it about constructing artificial bat habitat. Post questions to her blog as comments, and I'm sure she'll have plenty to say.
This panorama is composed of 12 segments, each photographed at three different exposures: 30, 8 and 2 seconds, all at f8 and ISO 400. Nothing less could produce useful exposures using only the dim, indirect light coming in through the entry tunnel. The images, totaling 364 megapixels, were assembled into three separate panoramas, which were combined into a single high-dynamic range image, then tonemapped down to a range that monitors can handle. Unfortunately, using only three exposures per segment still left the entry tunnel over-exposed, which is exactly the sort of thing that high-dynamic range photography is meant to prevent. My camera will only take three different exposures automatically, so taking additional exposures would have meant a lot of manual manipulation of the camera. Such manipulation brings with it the danger of causing the tripod to shift its footing, thereby ruining the precise alignment of the images. (The spiked feet of my tripod never did find the concrete floor - eventually I just made them stable in the guano.) That limitation may have been fortunate, however: the HDR and image manipulation applications that I depend on kept choking on the size of these images. In the end, it seemed like pure luck that I finally got them to do their jobs. An additional exposure or two might have prevented the tools from ever doing their jobs.
With the three panoramas finally combined into a single rectilinear image (360° by 180°), that image was broken into six images, corresponding to the faces of a cube. Doing so made it possible to heavily retouch the image of the floor to remove the tripod, the panoramic head and its counter-weight from the image. (In other words, the floor seen beneath the caption and copyright notice is an artificial construct.) The cube faces, including the heavily retouched floor face, were then combined to make the final QuickTime VR panorama.