Background:
In PA (and many other states) the location of quite a few sodalis hibernacula are known, but very few summer roost sites have been discovered. This has crippled landmanagers and biologists who are attempting to manage this species presumed habitat. In a effort to add a new trick to the decades old method of radio tracking bats back to roosts, we are attempting to trap sodalis at a known hibernacula, follow them through 10 to 12 days of migration and examine their roost preferences in that time span.
This particular hibernacula contains a low number of sodalis and they are using an area within the site that is at a higher temperatures than the species normally shows a preference for. This has lead to speculation that they may not be migrating very far. With the energetics of hibernating at a less than ideal temperature being more costly, the energy reserves for a long spring migration would be slim.
This may give us a shorter migration than one would expect in other areas of the species range, but we are not counting on it.........
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Here John Chenger fine tunes a seven element null peak array in horizontal configuration. The pole that attaches it to the van telescopes to 20 feet in height. |
The latest and greatest (i.e. largest we could mount on a vehicle) tracking equipment was selected for this project. In the test phase this particular array picked up a transmitter at a distance of 9 miles. This was under the most ideal circumstances we could find within the project area, but it goes to show how far tracking technology has come. A transmitter weighing less than half a gram, with a battery life of 10-12 days, that can be picked up at 9 miles!!!! Unfortunately most of the terrain in the area consists of very hilly and rugged geography where our range is limited by line of sight. In that region our strategy is to use three and four element antennas (quicker to setup) to increase the number of sites that can be checked by each team each day.
FAQ:
Q: What is the range of your transmitters?
A: Range is highly variable based on terrain. We are lucky in that the project area is centered on a ridge top, this will give us a some good long range scanning points. However blank spots in our line of site will require many points be sampled where our range will be limited to under a mile.
Q: Why do you think you can follow bats through migration, don't you think the bats will just stay around the hibernacula for the duration of the transmitters life?
A: Habitat, prey, energetics, and temperature. The hibernacula is on top of a relatively cold ridge with little in the way of water within a mile. Prey abundance is much lower around the hibernacula than down in the warm stream valleys below. Migration is costly from a energetic point of view, if there is suitable habitat within 10 or 15 miles, why migrate 200? In other parts of the species range it must migrate. In New England the best hibernacula are in the eastern mountainous regions of NY so bats with summer roosts from CT to Rochester NY are probably forced to migrate a long distance every spring and fall between these regions. In some southern hibernacula the bat populations are so large they must spread out so not to exceed the carrying capacity of their ecological niche. This hibernacula contains around 1,000 bats (all species total) and there is diverse roosting habitat within 25 miles. Predicting wildlife is a tricky thing, but in theory they should stick close.
Q: Don't you think the sodalis are already out? It's been a warm spring...
A: No, we don't. Check back around the 15th, if we haven't caught any by then we will be starting to worry..... We caught a smallfooted bat (Myotis leibii - state threatened) on April 1st. That's a pretty good indicator that the early emergers are not all gone.
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From: Rickard S. Toomey, III of Illinois
Q: By the way, any chance the late (or early, whichever 4am is) catches represent animals from outside coming into the cave as either a night roost or changing roosts? (This is in reference to the April 2nd update where I wrote we were still catching bats emerging at 4 am.)
A: Yes, that is very possible, however we had noted bats circling inside the tunnel, behind the traps, earlier. We only caught bats during breaks in the rain. This lead us to believe that the bats were active inside the tunnel, awaited pauses in the rain, and emerged then. It was still warm (50s) between 4 and 6am so they may have been coming out for a delayed feeding or it could have been entirely different bats attempting to enter the tunnel from the outside.
We are looking at long wave IR cameras/scopes to record this type of information. If anyone out there has one they could lend us so we can get a feel for it's usefullness we'd be very grateful. We'd also like to have LW IR so we can come up with % caught vs. manage to pass through information for our harp traps.
As usual our field work is raising many questions, are the bats that we catch at the beginning of storm fronts ones going in? (Some were.) Or does the barametric pressure/storm temperature change awaken them to come out and check the weather/re-calibrate circadian clocks? If they are coming from outside the hibernacula are they bats that had emerged from this hibernacula earlier or are they using the site as a migratory stopover/shelter? Much more work needs to be done on the migratory patterns of all bats. I hope that this project attracts researchers interests towards studying this aspect of bats life cycles. Hibernacula previously catagorized as unimportant may provide critical migratory stopovers for bats as they travel each spring and fall.
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Comments:
What a great site! I'm looking forward to following your progress. Good luck. ---- Annette Scherer, USFWS
Fantastic web sites. I enjoyed reviewing them this AM. ---- Bernie Holcomb, CH2M HILL
I'm enjoying the hell out of your web site. Keep up the pace. You guys are learning a lot. Nothing replaces the kind of experience you are logging. ---- Jerry Hassinger, PGC
I love the web page! It is definitely the {edited}!!!!!!!!!!!!!! Most righteous. I really like the explanations. I love the pictures too! The one of that newt was awesome. Oh, what's the difference between a newt and a salamander? {Try this newt link....} ---- Anonymous