A University of Florida study has demonstrated that Northern Mockingbirds can distinguish individual humans and respond to them based on whether they’ve previously been threatened by that specific human. In the study, grad students who poked at Mockingbird nests on consecutive days were subsequently hassled by the parent Mockingbirds, while grad students who had not poked the nest were allowed to approach much closer without being dive-bombed, shrieked at, or otherwise subjected to Mockingbird ire.
This is a remarkable ability for a bird with a brain maybe the size of a large honey-roasted cashew, and the researchers speculate that it may have contributed to the Mockingbird’s success in colonizing urban and suburban landscapes. Understanding which factors lead to the success of urban-dwelling birds is not only nifty in its own right, it can potentially offer clues on how to make urban and suburban habitats more congenial to less flexible species.
It’s a fascinating study, and the more I think about it, the more questions it raises. How do the mockingbirds do it? The grad students wore different clothes on different days of the experiment, so it’s not based on “plumage”. Either the birds can recognize distinct human faces/hair colors, etc., or it’s something more subtle, like gait or the timbre of the individual voice (Mockingbirds are, after all, quite good at noticing and remembering sounds).
And why? Has urbanization been around long enough to be a major selective pressure on Mockingbirds? Or is this a pre-existing trait now being adapted to a novel environment? And if so, what was it used for before people, with their puzzling propensity to poke nests, came along? It seems to me that once most predators know where your nest is, there’s not much left to defend for next time, so it’s better to go after all of them, not just memorable individuals – but I’m not a Mockingbird, so I could be wrong. Maybe preemptive aggression towards predators that don’t already know where the nest is only tips them off that there’s something interesting in the neighborhood.
Or perhaps this behavior drives away clumsy herbivores that might disturb or expose, not devour, the nest – say by preventing the local deer from making a particular shrub a regular snack-bar stop. In that case, it would be a waste of resources to hassle a deer that was just passing through.
Obviously, all this is just speculation and much further study is needed, which just goes to show that even common birds are worth careful observation. After all, it appears that they’re carefully observing us!
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May 20, 2009 at 6:40 pm
Quite often things evolve for different reasons then there current (or one of their current) uses would suggest. My brain may be capable of appreciating Mozart`s Magic Flute and the Ramones, but it is unlikely that that was the original impetus for a larger brain.
While Mockingbirds may be able to recognize individual people the natural forces at play probably were driven by some other selection pressures.
May 20, 2009 at 6:47 pm
Right, but that’s what I’m saying – what were those pressures? What specifically were these birds making this kind of fine distinction among before people came along?
May 20, 2009 at 9:19 pm
We’re kind of saying the same thing, but what I’m saying is that perhaps this ability is an accidental characteristic of completely different evolved characteristic of the brain.
As you point out Mockingbirds excel at identifying and remembering sounds, which quite possibly came about because of sexual selection pressures, an unintended consequence of that variation in the brain might have been increased visual clue recognition and memory. If the unintended characteristic didn’t confer any negative pressures it could be retained along with the originally selected characteristic.
I fear I’m not stating this well, and perhaps should have stuck to the original analogy of music appreciation. When we mutated a larger brain it was selected because it conferred a benefit to early humans, those with that mutation out survived those that didn’t, meanwhile a consequence of the larger brain, neutral in terms of its “fitness” came to be an appreciation of music. A bonus, if you will, to the “fit” of a larger brain in the world.
Perhaps the ability to recognize people in Mockingbirds is similar. Perhaps not, and at any rate you’re right, it is fascinating and begs more questions than it answers.
May 21, 2009 at 3:27 pm
Clare: I see what you’re saying now. I think we don’t really disagree; obviously the roots of the skill were in there somewhere. Although I’d be surprised if song memory also increased visual cue recognition – but then again, I’m no neurobiologist!
May 27, 2009 at 8:22 am
I think the intelligence of birds is often highly underestimated as humans tend to think that a brain’s effectiveness is based solely on its volume. Wrong. I still remember PCs about the size of a small trunk whose hard drives were in the range of a few 100 MB. Now we can pack 1 TB into a space the size of a pack of cigarettes.
Why is it such a surprise that Mockingbirds are able to recognize people individually? Every genetically deranged pet parrot can do it. “Pet” songbirds that were caught as wild birds can do it. Heck, even tiny pet mice can do it! Even if their owners change their clothes once in a while. So why should wild birds living out in the wild not be able to do it?
And I really don’t see why and how that ability should have anything to do with living in urban areas or be a prerequisition for colonizing the immediate surroundings of humans. Surely staying alive for as long as possible and raising as many young Mockingbirds as possible in a natural landscape is as demanding, challenging and complex as doing the same around human settlements?
Why can they do it?
Well, I suppose simply because they can.
Why can we tell individual birds / animals apart by their song, individual patterns or behaviour traits? Where is the evolutionary advantage for us, where the selection pressure on humans to develop that ability?
May 28, 2009 at 11:35 am
Well, admittedly that was a bit of a ranty comment for which I appologize.
You see, when I was young(er), the “concept” of viewing animals as “instinct machines” was still quite widespread. Many people would tell you that if you hurt an animal, it would not cry out of pain but simply because its instinc would make it utter those sounds – no emotions or feelings whatsoever, just a cold programmed machine.
When caught in such conversations, I always used the following line of arguments:
Me: A wolf is a wild animal and thus an “instinct machine”?
Other: Why, yes, of course.
Me: Do you have a dog?
Other: Yes.
Me: Would you say your dog loves you, misses you when you are gone, enjoys certain foods because it likes the taste of it, gets angry, is sometimes grumpy, can be affectionate…?
Other (smiling): Oh yes, my little doggie is just like that.
Me: But those are all emotions. So you are saying that a wolf is an instinct machine while your dog is showing emotions and social intelligence. Are you aware that genetically dogs are wolves and actually are genetically crippled and thus probably less intelligent and social than their wild ancestors?
Other: … well … but you see, dogs were bred from wolves and have only developed those traits because humans selected and bred them accordingly. They are new traits unique to dogs but not found in wolves.
Me: Aaaaaargh!!!!!
So whenever I read articles about new findings – big surprises – amazement all around – that a certain animal is
a) capable of intelligent actions b) social c) can recognize individuals d) can count e) can do whatever
I feel the urge to jump in the ring, fists raised and scream “Why is that such a surprise, you anthropocentric #$%&! Of course they can do it! Animals are better than you think!!”
Here, on this blog however, I realize I was preaching to the choir.
May 28, 2009 at 3:18 pm
No worries, Jochen. I know the type of people you’re thinking about.
It makes sense that any even slightly social species would recognize individuals that they saw as part of the social group, which pets tend to do with their owner. I’m more surprised that the mockingbirds extend this to predators. Sure, it saves some energy to not waste time scolding every human being that moseys by, but is the payoff in scolding the nest-pokers great enough to make it worth the time and effort of remembering them? Apparently so.
And, of course, with most mammals, the most reliable way to tell individuals apart is smell, which according to conventional wisdom isn’t an option for mockingbirds.
May 29, 2009 at 8:07 am
Carrie, I would say that being able to differentiate between individuals and not only species is something that must have developed very early in animal evolution. Look at birds: as one member of a breeding pair, it is a good thing to recognize your partner anytime anywhere or else you won’t know if you should let that bird get close to your nest to deliver food or chase it out of your territory. Many birds are paired for life, and e.g. goose families stay together even during their migrations from Siberia to western Europe and back. They migrate in flocks of several 1,000 individuals (I once encountered a flock of 120,000) and surely it helps recognizing your partner and offspring if you want to stay together in such a huge mass of conspecifics.
I would therefore guess that the ability to recognize individuals developed the moment animals evolved beyond laying eggs and walking/crawling off. The moment you look after your off-spring, be it as a pair or a “single” mother, you need to recognize them and/or your partner individually. And the moment you can do that, you can probably also – at least in theory – automatically recognize other animals as individuals. Whether you need it or not or draw an advantage out of it or not is a different matter. Possibly, there is an evolutionary step from recognizing conspecifics individually to doing the same with non-conspecifics. But I am certain this is not a big step.
July 3, 2009 at 6:19 pm
Please help me! We have a 5 acre-meadowlike lot which has been overtaken by mockingbirds!! They are nesting in pear trees and dive bomb my cat and very large dog-on occassion! They also are very noisy and have chased most of the other birds away. Today I saw a group (like a gang) of brown birds (I couldn’t tell, but looked like catbirds) come in a flock towards a few mockingbirds and then land on a fence near the fruit trees.
Is there anyway to move them away from the house, or to keep them quiet.
Thank you!
July 4, 2009 at 3:23 pm
Amy – The mockingbirds will not seriously hurt your pets. As for noise, I recommend earplugs or headphones. I can’t recommend trying to move or shush the mockingbirds, since interfering with a wild bird or its nest is a federal crime.