Walking back from the library today, BChester asked me to find the great blue heron which we saw on the way out and which lives in our neighborhood. We spotted it hunting voles along the path back to our apartment.
We stayed and watched long enough for the heron to get accustomed to our presence. BChester kept on saying "heron pretty!" and "heron cute!" as we watched it wander around looking for rodent holes to peer into. The heron apparently noticed a vole about 10 feet in front of us and decided to stalk it, ignoring us completely. He [it was a male] very slowly walked toward the vole in a heron's equivalent of a soldier crawl, with his neck folded up and so close to the ground that his neck plume was dragging in the dirt. When he was about a foot away from the vole he stopped and began adjusting his footing and angle to get the perfect strike. He further retracted his neck until it was wound up like a spring. BChester found this completely entrancing.
The heron soon struck. His neck sprung, propelling his head forward like a viper, and he used his hefty and razor-sharp bill as a spear. We could distinctly hear the sound of rodent bones being crushed [if you haven't heard this sound before, it actually is quite distinctive]. He immediately calipered the vole by the neck and lifted it off the ground.
But at this point, the heron was out of tricks. He had to wait for the vole to bleed to death since he had no built-in way to off rodents like most specialized rodent-killers do [watch a prairie falcon casually rip the spine out of a ground squirrel some day, it's easy for them]. After several minutes, the vole turned its head around and started to gnaw on the heron's beak. I imagine a bone saw would make a similar sound. Eventually the heron got tired of that and threw the vole back on the ground, wound his neck up, and piked it right through the skull. The vole didn't move much after that.
We then watched [BChester: "heron lunch"] the heron orient the vole nose-down and swallow it whole. At one point the vole got stuck in the bottom of the u-curve section of the heron's throat and we watched him contract his whole neck over and over again to try to get it down ["heron play"]. But then it was over. BChester didn't want to leave but once the vole was down it was obvious that the heron didn't want any more company.
Besides a thrilling up-close look at some serious natural carnage, this experience got me thinking about some pretty profound evolutionary messages hidden in this behavior.
The great blue heron is a fantastically well-adapted bird--for stalking fish in shallow water. The entire genetic code of herons is calculated for two things: fishing and sex [what a life, eh?]. The long legs keep the body elevated above water, the long neck helps them reach into the water without submerging the body, the long beak helps them catch fish, etc. Herons can catch a fish, toss it into the air, catch it when its head is oriented the right way, and swallow it in under a second and without rippling the water. They have extensive in-built hunting techniques which assist them in stalking fish, utilizing light and shadow and fish behavior. The cumulative effect of all of these features is that of a very refined and polished masterpiece of evolution.
Except...
Our bird was hunting on dry ground for voles. The stalking method, the attacking method, the killing method and the eating method that I witnessed are all completely different than the way they stalk, catch and eat fish. The special adaptations that herons have for hunting fish put them at a disadvantage when hunting voles. Their long legs and large body make them conspicuous and hard to hide, they have no way to kill prey quickly, and there are few voles swimming around in the shallow waters at the edge of bays, which is where herons should be programmed to try and find food.
The first observation is a simple one: animals are not stupid. The popular consciousness [such as it is] has held for a long time that genes control everything about an individual animal's behavior and capabilities. Besides being anthropocentric, blatantly contrary to common experience and logically ludicrous, this idea is also the foundation of a litany of corrupt philosophies about human nature. And most conscious biologists would find the idea appalling. If genes controlled all the behavior of every member of a species herons could never hunt voles. Somewhere at some time, this bird or one of its ancestors discovered a source of calories and through trial and error devised a hunting technique that would work for voles. This requires thought. Perhaps rudimentary thought, but thought nonetheless.
Now that that's out of the way, there are some more interesting things to talk about.
We're taught [if at all] that all traits are the result of millenia of selection events. The truth, as pointed out by Stephen Jay Gould, is that some features are "spandrels;" excess baggage created by genes which control other features which have been selected for. These features then have not been selected for even though they exist. Some features arrive through "exaptation;" adaptations co-opted for new beneficial uses. Think about our ability to wipe our butts, which was not the evolutionary impetus for hands but is a great use for them.
It appears that this heron has used some amount of general intelligence to co-opt their specific fish-catching adaptations [I'm thinking the lance-like beak] to catch voles, a perfect example of exaptation. This required, in the least:
1. Recognizing voles as a source of calories
2. Devising a strategy for stalking voles
3. Devising a strategy for catching voles
4. Learning not to swallow the voles until they die
Since I actually have seen two distinct herons in this area do this, I can add another one:
5. Teaching others steps 1-4
I'm not claiming herons are terribly bright. And I'm not claiming this is particularly new, it's actually rather old news as far as evolutionary biology is concerned. But what did impress me is that it took evolutionary biology until 1982 to recognize what was supremely evident in this heron; that adaptation and natural selection are only a portion of the whole evolutionary picture.
Suppose there is enough habitat in the bay area to support a couple hundred full-time vole-eating great blue herons for dozens of generations. Then we could see a subset of the population break off and eventually parapatrically speciate. That means that they could form a mostly isolated gene pool which will slowly acquire traits beneficial to vole hunting and thus diverge from main-stream herons and become its own species. The new niche is actually not new, it's just nearly infinite; there are not enough snakes, raptors, and coyotes in the area to make a dent in the vole population.
The heron I saw was so successful [killed in one attempt; 90% of the raptor attacks I see are failures and they all use lots of energy] that I can imagine it turning out that only one or two genes need to be changed to make the herons the most efficient vole-eaters on the planet; none of this wasteful hovering like kites and none of the slow dangerous slithering of snakes. Classic Darwinism pictures species arriving at an optimal form always from the bottom-up, arriving through branches of selective adaptations after millenia. The concepts of spandrels and exaptation allow hopping from limb to limb on the evolutionary tree in a way that creates species laterally. We're not talking about herons moving to enjoying crustaceans here-I'm talking about a change in almost every non-morphological phenotypical aspect of a species in one shift occuring over only a few generations. And these behavioral and environmental changes will surely lead to accelerated genotypical shifts due to the extreme "distance" between the niche evolved in and the niche moved into. This strikes me as a much more efficient way of generating diversity than classical adaptation, even if the conditions for exaptation have to be just right. The catalyst for using exaptation this way is general intelligence. In that way I'd expect the diversity of life on this planet to be much smaller if animals were thoughtless robots as popularly assumed.
This, in a nutshell, was half of what I was thinking when I saw the heron, beak sheathed in dripping blood, saunter away from the killing site. The other half was this:
Holy son of beelzebub!
Subscribe to:
Post Comments (Atom)
6 comments:
Comment posted from V:
Excellent little essay...very thought-provoking. Let me postulate one other explanation for vole-eating: besides general intelligence, which allows the heron to identify the vole as edible and allows the heron to improvise a new hunting strategy, I think we also have something we could call "incomplete specialization" in the heron's evolution: Before herons wer fishers, before they were identifiable as a separate species per se, they were generalists, as all origin species are. Is it possible that herons, in becoming specialized wade-stab-toss-swallow fishers never lost their generalist ability to hunt voles, which, as you note, is highly conducive to species survival in at least some environments? THis scenario allows the possibility that any specialized species will have a PREFERRED mode of food-acquisition, and several backups for which it is perhaps less perfectly-suited but which suffice in a pinch.
Anyway, your model of branch-to-branch lateral speciation [or at least behavioral specialization] is compelling and clear.
To strengthen the essay, I would find a more survival-conducive example of exaptation than butt-wiping. What did hands evolve FOR, anyway? They are one of the most generally useful adaptations, and it is important to remember that we evolved in a very resource-scarse environment, which is why we are such robust generalists. Specialization, says the orthodoxy, is the product of two things: plentiful resources and geographic isolation. Which also leads to fragility. Herons have such a huge geographic range that they must be the inheritors of come general skills, and they ar so adapted to water-edges [which are unreliable and highlky variable] that they must have back-up plans... had they evolved in the rain-forest of Costa Rica they may not have maintained the vole-spearing behaviors...
Anyway, just some rather unformed thoughts, maybe fodder for a future essay?
V.
I always thought the length of arms was interesting. They get the hands where they need to be used. The only thing they can't reach - in my experience anyway - is the middle of the back, which is what trees are good for, I think: not too much happens back there that a good tree can't 'handle' well.
I wonder as we all grow rounder if average arm-length will increase.
The question you both raise is an interesting one with wide implications: is the Great Blue a wader-fisher? Or is it a stalker-jabber? The first is what we mostly see, but does that mean it came first?
Our local favorite Great Blue adapted the wader-fisher technique opportunistically: he hung out under a 'street' light on the dock our boat was moored to and fished by jabbing from there. He never got his feet wet. His mom never taught him that, and it's not part of his wiring either.
What is general intelligence? Elastic gray cells? I believe it.
Our dog Gimli loved to communicate w/ his people. He had all the body language of a dog, and an unusual capacity for escape, but the most non-dog experience I had with him was when he tried to communicate. He got an intense look on his face and in his eyes that just begged to be understood. He was propelling thoughts in my direction with focused energy and earnestness. He was stuck in there without anything more than his body and eyes as means of expression.
My reaction was to try to interpret for him: you want to play ball? (Off he'd go to get it.) You want to go out? (He'd sit down and continue to throw thoughts at me.) You want to run in circles around the house w/ me chasing you? This I conveyed by lunging at him. (Off he went to be chased.)
Was I (sometimes) a good guesser? Or was he successful in penetrating my skull...?)
What about Korean or Chinese dogs, I wonder? The ones that are eaten? Do they have the same kind of thoughts? The Chinese kids I talked to explained that they were: 1) a different kind of stupid dog, or 2) strays. And it was ok to eat them. I think that means they were dogs no one ever talked to.
So how did dogs get this way, where they understand language - I mean verbal people language? Where did they get such a large vocabulary? They must have general language from being pack animals, just as whales must from being in pods (though I don't know about cattle from being in herds - though maybe they live so unnaturally now that there's not much to be said).
I'm talking about general language in parallel w/ general intelligence.
I just read in Omnivore's Dilemma that koalas now have smaller brains than they used to because they don't have to figure out what to eat. Or I suppose it can be that they eat this one kind of eucalyptus because their brains shrank for another reason: in any case, today's koala skull is way too big for today's koala brain.
Skull size evidently doesn't change rapidly, so what if dogs are limited by that flat little skull? Are those skulls growing?
Anyway, what is language? A general trait? And what is general intelligence? And how are they related?
I always felt that the ambush strategy was a more effective method of hunting than the pursuit strategy, anyway.
Well "effective" implies quite a bit. It's certainly more efficient in marginal circumstances and given a somewhat limited supply of prey, especially if the animal is cold-blooded. But in order to even enter some niches warm-blooded predators absolutely must pursue.
I guess this statement would be more or less true, though: given a prey species available to both ambush and pursuit, a cold-blooded predator will certainly--and a warm-blooded one most likely--find a better calories-received/calories-spent ratio with ambush techniques than with pursuit strategies. Not very catchy, eh? I can't think of a stronger statement that would be indiputably true though.
My terminology is at fault; I did mean efficient (I think you've reproached me on the distinction before) and I think the method the heron used is still considered to be a variant of the pursuit (stalk-run-pounce, as it's called with cats) method.
Ok, I'm finally ready to answer.
V: I agree about the "incomplete specialization" thing, except that I'm not too sure about the idea that all origin species are generalists. The macroscopic trend certainly is toward finer and finer niche distribution, but on a species-by-species basis I can't see that being a general rule. At the very least, the primordial ooze contained the most specialized of all organisms. The Permian explosion was arguably the result of adaptations toward generality.
Anyway, I think there is a lot of truth in what you said. It is highly unlikely that our heron is the first heron in his lineage to discover that voles are easy. There's certainly enough in here for another essay down the line.
M: The answer to your last question, at least, seems clear from the material I've read. Language is "equally" a product of specific programming and general cognition. And the most recent research says it is most likely not a "trait" as much as a pastiche of exapted traits and spandrels. Without innate grammar we'd never learn the rules of language and without massive general cognition we'd never even get as far as to learn where the breaks between words in a string of speech are.
thanks for the comments!
Post a Comment