Not Exactly Rocket Science

Blogging on Peer-Reviewed ResearchWhile the rapid expansion of human cities has been detrimental for most animals, some have found ways of exploiting these brave new worlds and learned to live with their prolific inhabitants. The Northern mockingbird is one such species. It’s very common in cities all over America’s east coast, where it frequently spends time around humans. But Douglas Levey from the University of Florida has found that its interactions with us are more complex than anyone would have guessed. 

i-610c19ba71197528bb9c888aa4399e66-Mockingbird_divebomb.jpgThe mockingbird has the remarkable ability to tell the difference between individual humans, regardless of the clothes they wear. After less than a minute, they can tell one person from another and adjust their responses according to the threat they pose to its nest. This ability suggests that these birds are both intelligent and very flexible in their behaviour – two traits that must surely stand them in good stead in the urban jungle.

It obviously benefits an animal to be able to distinguish between threatening and harmless species, but discriminating between individuals of the same species is a much more difficult task – just think about how difficult you would find it to tell the difference between two mockingbirds by eye.

Levey worked with 24 pairs of mockingbirds that had taken up residence on the university’s campus. Hundreds of people walk within five metres of their nests every day and elicit absolutely no reaction. To simulate a greater threat, Levey asked one of his colleagues to approach the nests of birds with fresh clutches, and touch their rim for 15 seconds. When faced with such intrusion, mockingbirds will typically react by rallying from the nest, making alarm calls and diving aggressively at the trespasser.

i-00b19f64c7f3414422286df99fb47693-Mockingbird_recognise_indiv.jpg

Initially, the same intruder approached the nest for four days in a row, each time wearing different clothes. Despite their changing garments, the birds seemed to recognise them and reacted more aggressively as the days went by. They flew from the nest when the human was further away, they make more alarm calls and they were more likely to attack.

That could simply reflect a generally rising state of panic, but the events of the fifth day put paid to that idea. At that point, the intruders swapped and a different person approached the nest in exactly the same way. Faced with this new intruder, the birds reduced the degree of their alarm to the level of the first day. To Levey, this simple experiment clearly shows that the mockingbirds quickly learned to recognise people who approached their nest.

i-31df157dbde8cadf074407ea4d740618-Mockingbirds_recognise.jpg

Many animals can tell the difference between individuals of their own species. But, anecdotes aside, there are relatively few reports of them pulling off the same trick with members of other species. Chimps can apparently do it from photos, prairie dogs from sound and cattle from smell. And animals from pigeons to honeybees have shown some skill in distinguishing between photos of humans in experimental conditions. But the mockingbirds in Levey’s study passed a very realistic and difficult test – they had to tell one individual apart from thousands of others, all of whom changed their appearance on a daily basis.

They also did it with incredible speed. Within just two approaches by the human intruder, each one lasting just 30 seconds, the birds started behaving more aggressively. This means that a mockingbird can learn to recognise a new individual within less than a minute. In virtually all studies where other animals have learned to identify or classify individuals of other species, they have required 10-1000 times more training.

i-3b9dda9243e1455ada0fb31eccf0709f-Mockingbird.jpgThe fact that a songbird like the mockingbird can do this strongly suggests that other birds can do the same. In particular, the intelligentsia of the bird world – crows, jays and parrots – should be all too capable of distinguishing between individual humans.

If mockingbirds can tell the difference between individual humans, it’s likely that they can do the same for individual cats, raccoons and other egg thieves. Indeed, it will be interesting to see if rural mockingbirds have the same ability. But Levey doesn’t think that the urban populations have evolved a specific ability to tell humans apart. Rather, he suggests that mockingbirds are generally perceptive and learn quickly, traits that allowed them to colonise urban environments. Moving from rural areas to the big, bad city poses many unfamiliar challenges, including many new predators intending to kill a mockingbird.

Reference: Levey, D., Londono, G., Ungvari-Martin, J., Hiersoux, M., Jankowski, J., Poulsen, J., Stracey, C., & Robinson, S. (2009). Urban mockingbirds quickly learn to identify individual humans Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.0811422106; images by Calibas and Mdf

More on bird brains:



i-77217d2c5311c2be408065c3c076b83e-Twitter.jpg i-3a7f588680ea1320f197adb2d285d99f-RSS.jpg

Comments

  1. #1 Jefrir
    May 19, 2009

    I’m pretty sure blackbirds can do the same thing. The ones in the garden will hang around if my mum (who feeds them) comes out, but fly away from anyone else. As I look pretty similar to my mum, and it doesn’t seem to make a difference whether I’m carrying bird food or not, it seems that they’re recognising an individual.

  2. #2 psycho
    May 19, 2009

    “just think about how difficult you would find it to tell the difference between two mockingbirds by eye”

    But birds are much smaller, there isnt that much difference (as in case of humans) when it comes to one specie, I believe.

    However, in case of bigger animals, such as elephants, I do wonder what’s the cause.
    Are elephants more similar to each other than humans are?
    Or is it because of adaptation?
    Or is it both?

    (btw, when I was a child, I remember having problem to tell difference between people of other races – that’s plus for the ‘adaption’ point)

  3. #3 deang
    May 19, 2009

    A mockingbird attacked me a couple of days ago here in Austin, TX. I was walking past some young Retama trees (Parkinsonia aculeata) and suddenly there was this mockingbird hovering by my shoulder and rushing at my arm, sort of head-butting me. It sounds kind of funny but it actually scared me a little. The bird did it repeatedly for about a block before flying back to the Retamas. I rarely walk that way and I don’t bother birds, but it is fledging season, so I’m guessing there must have been a baby mockingbird in those trees. The mockingbirds by my home have a chick, too, but they never bother me.

  4. #4 John Wall
    May 19, 2009

    It wouldn’t be adaptive to raise an alarm for non-threatening individuals. It’s risky to bring attention to yourself. I hope the experimenters didn’t unwittingly bring trouble to the birds. And speaking of alarms, we had a mockingbird one year that would mimic a car alarm, right down to the beep at the end.

  5. #5 humorix
    May 19, 2009

    It is all opposite with women! (when they touch has their small nest)

  6. #6 JJ
    May 19, 2009

    Admit it, the research project and the resulting article were all just to build up to the “To Kill a Mockingbird” reference.

  7. #7 Ed Yong
    May 19, 2009

    Got me. I’m just glad that ten years of putting my money into funding mockingbird-related projects has paid off at last.

  8. #8 GodlessHeathen
    May 19, 2009

    I have a Western Scrub-Jay friend who definitely picks me out from the crowd. I’m continually amazed that he knows it’s me whether I’m riding my bicycle or on foot, wearing a bike helmet or not, with another person or alone. He recognizes me and flies toward me from up to 200′ away. The sidewalk/bike path is continually full of pedestrians and cyclists, so I often wave at him to get his attention. However, many times I just turn and notice him flying alongside my bike as I ride to our peanut-feeding spot. I know that he does not visit people randomly and I can only guess how he instantly recognizes me among the hundreds of people he sees each day.

  9. #9 Markk
    May 20, 2009

    Does the study distinguish between recognition of individual people or specific actions? In other words are the birds reacting to specific actions that anyone could do or specific people? This is hard to tell apart, the people approaching the nest may make certain gestures or motions, turning and so on. This could be accounted for, eg, by having different people try to mimic the nest approachers actions. Was that done?

  10. #10 K. Signal Eingang
    May 20, 2009

    I recall a story some time ago where a school bus driver in Ohio (or maybe it was Indiana?) had taken to feeding the local crows on her lunch break. The crows not only recognized her but came to recognize her bus as well – she nearly lost her job when the birds started ripping windshield wipers and various rubber seals off the bus out of boredom as they waited for her to come out and take her break.

  11. #11 CatBallou
    May 23, 2009

    I love you, Ed, but “rapid expansion …have been detrimental”? Really?

  12. #12 april
    May 26, 2009

    How many different kinds of mickingbirds are there.whats the different types and what are there distinctions?

  13. #13 Andy
    August 10, 2009

    Broadly speaking there are 2 types of mocking birds. One is the Northern Mockingbird, as mentioned in the article and the rest can be classified as ‘Others’. The only obvious distinction is all of them are 4 times more intelligent then you except for the one mentioned in the article … which is just twice as intelligent as you.

The site is undergoing maintenance presently. Commenting has been disabled. Please check back later!