Night roost

The sandstone cave yielded 602 photos, but only 274 were of animals.

The low success rate of 46% was due to false triggers caused by bats.

They zipped in and out of the cave seeking a place to settle, and this triggered the camera.

Even so, we got 117 bat photos, and this yellowish brown bat with biggish ears was the most commonly photographed species.

Two species fit the bill -- the big-eared myotis (Myotic evotis) and the fringed myotis (M. thrysanodes).

The distinguishing characteristic, a fringe of hair along the interfemoral membrane would make it the latter.

None of the photos is clear enough to see it.

I am not confident of this identification, so this is a call to any mammalogists out there to speak up.

Deer, flies, bats and phlebotomy

Chuck Gackstetter, a year-round camera trapper from southwest Minnesota was good enough to send me this amazing image. It was taken with his home-brewed camera trap, a Sony P41 with a Snapshot Sniper control board in a camouflaged Pelican case. (Thanks again, Chuck.)

Most of the insects look like mosquitoes, but the lighter-colored ones may be deer flies. (Entomologists please weigh in).

If that doe was running from the insects, she's didn't seem to be shaking them off.

A picture like this makes you wonder how much blood a deer loses to mosquitoes. I recall reading long ago that arctic mosquitoes could actually kill a caribou. It sounds a bit far fetched.

Mossies can double their body weight after a blood meal, and the mossie known as Culex pipiens pallens sucks as much as 7.1 milligrams of human blood at a time. Thus, a thousand mossies could siphon off about 7 grams of blood, or a quarter ounce. That doesn't sound lethal. It would take a lot more than that to drain a deer to the point of death, but I am not going to claim it is impossible.

So what about Minnesota's deer gleaning bats -- the ones presumbly feeding on blood filled mosquitoes? Up there in northern Minnesoata, Willy4003 posted yet another picture of a bat and deer. (You may have to register with Pixcontroller to see it-- not to worry, it's free.)

It's known that mosquitoes (Anopheles gambiae, to be exact) fly more slowly when carrying larger blood meals than mossies with smaller payloads. They are also more vulnerable to predation by jumping spiders.

And bats? It seems likely that insectivorous bats can discriminate blood-fattened from light-weight mossies using sonar, and may also find the fat slow ones to be easier pickings.

Is this the route that led to phlebotomist bats? If eating blood-sucking insects gave ancestral vampires a taste for blood, how did they make the transition to biting the insect's prey?

The most likely explanation is that they started to feed on insects that were in the act of drawing blood themselves. If so, it seems more likely that the parasite was not a mosquito, but a biting fly like a tabanid. (Blood sucking leeches seem far less likely candidates).

Why? Because biting flies leave bloody wounds. Mosquitoes are better phlebotomists. They don't leave a trace of blood unless crushed on the spot. Bat eats blood-bloated fly . . . bat licks bloody wound . . . bat nips skin . . . bat becomes vampire. That might have been the evolutionary scenario in deep time.

PS: I would have liked to consult the literature on this topic, and apologize for arm chair theorizing. I realize that another route to vampyry is for a bat specializing on small mammal prey (like Megaderma spp) to switch to increasingly larger prey. If any readers can refer me to relevant references on this, please let me know. I'll chase down the refs next time I am in the bay area.)


References

Bekku, Hisao. 19__?. On the amount of blood taken up by a female mosquito of Culex pipiens pallens Coquillett, Nagasaki Iggakai Zassi, XXVIII(9):1036-7

Roitberg, Bernard D., Mondor, Edward B., and Tyerman, Jabus G. A. 2003. Pouncing spider, flying mosquito: blood acquisition increases predation risk in mosquitoes. Behavioral Ecology, 14(5): 736-740

Minnesota's deer-gleaning bats

Are insectivorous bats attracted to mosquitoes attracted to deer? Apparently they are.



Willy4003, a serious recreational camera trapper from Floodwood, Minnesota got me to thinking about this when he posted recent photos of bats and deer on the Pixcontroller Forums, and he kindly gave me permission to post them here.

Willy's cam was set at "an established mineral lick surrounded by ash and spruce near a marshy lowlying area, hence the extensive mosquito population." His photos were taken between 9:28pm and 12:18am on June 16th, and July 6th and 7th.

I put the question to my old mammalogist buddy Don Wilson, who is a bat aficionado of the first order. He responded: "I haven't ever heard of anything like that. Seems especially unusual in Minnesota, where the species diversity of bats is low, and foliage gleaners are not at all common. Very interesting."

The term "foliage gleaner" (not yet in Wiktionary) refers to birds, bats, and insects that forage for insects in vegetation by hovering, swooping, darting, and diving at their prey.

Deer are powerful mosquito bait, and they also play into the life cycle of a number of other dipteran (fly) parasites, like nasal and skin bots. Biting flies and mosquitoes couldn't ask for a better host than a deer in summer, when the thin coat renders most of the body vulnerable to blood-suckers. This cropped photo shows the mossies tanking up, and judging from the red spots, this doe probably has an itchy udder.



Of course, the bat-deer association could just be a coincidence. The bat might have just been flying by. But I have the feeling that if camera trappers had faster cameras, there might get a lot more pictures of bats and deer.



It goes to show, there's still plenty of natural history to be learned, and camera traps are a good way to do it. A hat tip to Willy 4003 for sharing this neat finding.