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Robotic Squirrels Battle It Out With Rattlesnakes
Hugh Pickens writes "Alasdair Wilkins writes that when a squirrel encounters a rattlesnake in the wild, it does something very peculiar to survive its brush with the predator — something is so peculiar that scientists are building robotic squirrels just to try to understand the behavior. A live squirrel does two things when it sees a rattlesnake. It starts moving its tail in a flagging motion and actually heats up the temperature of its tail. Because rattlesnakes can see in the infrared wavelengths, they should be able to see both the tail move and heat up. The question is which of these two signals is important and just what message it's supposed to send to the rattlesnake. To that end, engineers at UC Davis have built robosquirrels, which allow the biologists to simulate the two squirrel behaviors one a time and the research so far suggests it's the heated tail, not the flagging motion, that the snake responds to, making it one of the first known examples of infrared communication between two distinct species. 'Snakes will rarely strike at a flagging adult squirrel — and if they do they almost always miss,' says Rulon Clark, assistant professor of biology at San Diego State University and an expert on snake behavior. 'In some cases, it seems the rattlesnakes just decide it's best to cut their losses after dealing with these confusing critters,' adds Wilkins, 'as sometimes the snakes just leave the area completely after encountering these flagging, tail-heating squirrels.'"
... the tail wagging evolved to attract strikes from snake species that target movement, while the "heating tail" evolved to attract strikes from species that target heat (like rattlers). Maybe in the daylight it will be the wagging that saves the squirrel. Perhaps, if the waggging has no effect on squirrel survival, it's a leftover from an earlier evolutionary stage, where the snakes didn't have the infrared targetting capability.
A live squirrel does two things when it sees a rattlesnake. It starts moving its tail in a flagging motion and actually heats up the temperature of its tail. Because rattlesnakes can see in the infrared wavelengths, they should be able to see both the tail move and heat up. The question is which of these two signals is important and just what message it's supposed to send to the rattlesnake.
Its not sending a messages. Its presenting a decoy target.
I have had pet snakes for the last 10 years of various species, some with IR receptors.
Big warmed things tend to trigger the "too big to eat" response in snakes. That is, as long as they are moving. Stationary dead but still warm prey, may be looked upon as "luck, I found myself a free meal".
Most poisonous snakes tend to either not inject venom at all, or tone down the dose considerably when attacking as a defensive movement. Hence, even if the snake seems to miss, it might actually have hit and bitten, but no big damage is done. Making yourself too big to eat is an advantage even if it comes to a fight for the squirrel. For the snake, it makes no sense to waste valuable poison on something you can't eat, so just a warning dose will be more economical.
The squirrel can counter-attack and bite the snake behind the head if it attacks the big moving warm thing just next to the tail. There is plenty of evidence on youtube they do just that.
It will take quite some robotic squirrels before you can statistically prove these things, but I'm fairly certain most of these logical assumptions will be backed up by numbers.
I was promised a flying car. Where is my flying car?
Interestingly, it turns out that the squirrels (North American ground squirrels, in this case) are even cleverer than that, as the same team at UC Davis have previously shown. When confronted with a snake with infrared sensing organs (i.e. a pit viper, of which rattlesnakes are one variety), they engorge their tails with blood to send that infrared decoy signal. However, when they meet up with other kinds of non-infrared sensitive snakes (e.g. gopher snakes), they only flag with their tails; they don't use the infrared trick as well:
Squirrels wield a hot secret weapon
Why the difference? Presumably because it costs energy to send blood to your tail, where it then cools as it sends out its infrared signal. Thus, in evolutionary terms, it only makes sense to incur that cost if it has an advantage. Since gopher snakes can't sense in the infrared, why bother?
Of course, with respect to the current findings, it suggests that both flagging and infrared decoy measures are important to a ground squirrel, not just the infrared part. Otherwise, why would they bother flagging? Perhaps just because they have fun annoying snakes ...
And while the snakes might come off as just dumb reptiles in this story, let's not forget that those infrared sensing organs are pretty amazing as well. They have limited spatial resolution, but extraordinary temperature resolution, down to 0.001K. Indeed, once upon a time as a PhD student, I calculated that if you strapped a rattlesnake to the back of a 4 metre infrared telescope (!), it could detect the signal from Eta Carinae, one of the brightest infrared stars in the sky. Strap on thousands of rattlesnakes and count when each one rattled its tail, and you could take images :-)
definitely ig Nobel worthy