Category: behavior

Stunning duets in a neotropical wren

November 14, 2011 • 5:58 am

There’s a new paper in Science, brought to my attention by Ritchie S. King in the New York Times, that describes an amazing behavior in plain-tailed wrens (Pheugopedius euophrys). The species is neotropical: found in tropical forests in the mountains of Peru, Ecuador, and Colombia.  Here’s a photo from Wikipedia:

What’s amazing about this species is that the duet sounds like a single song, but actually consists of males and females alternating “syllables” at a rate of up to six per second.   When the female’s song has a tiny gap, the male fills in.  You can hear all this in the video below, and I’ll embed some songs from the paper.  The function of these songs is unknown, but they are probably involved in joint defense of territories.

The researchers, Eric Fortune et al., spent several months in the bamboo forests of Ecuador, recording wild and captive birds.  They also did playback experiments using “artificial song”.  The main results are described very well in this three-minute Science video below, presented by Fortune.  You’ll hear the duets as well as the single songs of one sex, showing the gaps that are filled in by the partner.

The authors found that the partners don’t just sing a stereotyped song, but adjust their songs to fill in whatever gaps are provided by the partner.  In other words, they’re sensitive to audio feedback from their mate, and, as the authors note, “are not relying on fixed-action patterns in the brain to generate duet song.”  As Fortune notes above, the female seems to play the “lead” in these songs, much like a partner who leads during a waltz.

Now I’m not sure if you can see this for free, but I’ll put the links to two movies of caged, duetting wrens. Below each movie is a sonogram that shows which partner is contributing which syllable.

Movie 1. “Top bird is the male wren, bottom the female. At the bottom is an oscillogram with the male and female parts marked in blue and magenta, respectively. The female initiated the duet, and the male moves its beak in its first interval but did not produce a syllable (1.11 to 1.36 seconds in the movie).”

Movie 2.  “This movie shows duetting in a captive pair of plain-tailed wrens. The bird visible at the start of the movie is the male, and the female becomes visible in the upper right hand corner. At the bottom is an oscillogram with the male and female parts marked in blue and magenta, respectively. Singing-related movements can be seen in both birds, but is particularly evident in the tail of the female at the end of the duet.”

And some audio recordings from the paper, showing both duets and single-sex songs:

Audio S1 Audio recording of the plain-tailed wren duet song shown in Figure 1A.
Audio S2  Audio recording of the solitary female plain-tailed wren song shown in Figure 1A.
Audio S3  Audio recording of the plain-tailed wren duet song shown in Figure 1B.
Audio S4 Audio recording of a solitary male plain-tailed wren song shown in Figure 1B.
Audio S5 Audio recording of a plain-tailed wren duet song in which the male skips a motif, as shown in Figure 1C.

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Fortune, E. S., C. Rodríguez, D. Li, G. F. Ball, and M. J. Coleman.  2011.  Neural mechanisms for the coordination of duet singing in wrens.  Science 334:666-670.

Computer chip replaces cerebellum in a rat

September 30, 2011 • 10:20 am

The amazing results reported in this piece from New Scientist, “Rat cyborg gets digital cerebellum,” haven’t yet been published in a scientific journal, but were reported in a meeting in the UK.  The details are sketchy, but scientists apparently built a computer chip using information from the inputs of a rat’s brainstem to its cerebellum as as well the output generated by its input.  (The cerebellum, a lumpy part of our brain located underneath and at the rear, is, among other things, responsible for motor control of the body based on input from the brainstem.)  How they got this information onto a chip is also unclear to me, but I trust some readers will enlighten us.

Once they made the artificial cerebellum-chip, they used it to see if it could substitute for the real one in an elementary brain-processing task.  As the journal describes:

To test the chip, they anaesthetised a rat and disabled its cerebellum before hooking up their synthetic version. They then tried to teach the anaesthetised animal a conditioned motor reflex – a blink – by combining an auditory tone with a puff of air on the eye, until the animal blinked on hearing the tone alone. They first tried this without the chip connected, and found the rat was unable to learn the motor reflex. But once the artificial cerebellum was connected, the rat behaved as a normal animal would, learning to connect the sound with the need to blink.

The journal also reports that another group used electronics to replace lost memory in rats.

While there are substantial differences in how brains process information versus computers, there isn’t any reason why computer chips couldn’t replace many of the functions of the brain.  It’s intriguing to contemplate, for example, the possibility that a computer chip might one day help blind people to see, or improve memory in those with diminished capacity.

A striking case of predator avoidance in fish

September 30, 2011 • 5:38 am

This YouTube video, sent in by a reader, shows how a school of fish reacts to hunting behavior of blacktip sharks (Carcharhinus limbatus) off the Maldive Islands.

Notice how the fish seem to move in a coordinated fashion, almost as one, and how they tend to group behind the sharks, where they’re less liable to be nommed.  Such “coordinated” group movement is not unusual in flocking animals; we’ve seen it before in the amazing behavior of flocks of starlings (see the videos here).  The thing is, biologists don’t really understand what cues animals use when groups of them appear to move as one.

It hasn’t escaped my notice that the sharks seem to be driving the fish toward the wharf, perhaps to either trap them or stun them against the pilings. (Dolphins, by the way, sometimes stun prey by whacking them with their tail.)

I asked my colleague Steve Pruett-Jones to watch it and, as an animal behaviorist, send me his take. Here it is:

Animals form large groups for many reasons, from reproduction to migration to avoidance of predators. Some of the largest groups of vertebrates are seen when birds flock and fish school as an anti-predator defense.

This amazing video illustrates the apparent coordinated movement of individuals in a large school, although in fact the movement of each fish is thought to be independent. How the fish do this remains somewhat of a mystery. Obviously, vision is critical (fish don’t or can’t school after dark, and fish that have been blinded also don’t form schools) but fish also often have prominent markings on their shoulders or tails (schooling marks) which appear to serve as reference marks indicating their movement.

Other possible cues include pheromones, sound, and the sensitivity of a fish’s lateral line. Fish that have had their lateral line removed swim closer together, suggesting that the lateral line keeps fish at a minimum distance from each other; fish appear to be able to ‘feel’ when another fish comes close because the lateral line is sensitive to pressure. In contrast to the fish avoiding the sharks in this video, the movements of the sharks are clearly coordinated as it is in many predators.

By “independent” above, Steve means that the fish are not all responding to a single external cue (which may in fact be what the sharks are doing when they make their “hunting rush” in this video), but to the presence of surrounding fish.  This suggests two things: first, that this “coordinated” behavior is really a response to the movement of a single individual, who sets off a wave that propagates through the group.  Second, the speed of propagation seems much faster than can be explained by the sum of the reaction times of all the individuals.  The fact is that we simply don’t yet understand how this type of group movement works.  That seems like a simple question, but it’s a simple question that’s hard to answer.

h/t: Krishan

The pace of life: a crazy idea for an experiment

September 30, 2011 • 5:13 am

“The pace of life” was the title of a 1976 paper in Nature in which Marc and Helen Bornstein did something very simple: they went to 15 cities in Europe, Asia, and North America, and simply measured the rate of walking of unwitting subjects over a marked, 50-foot stretch of pavement on sunny days of moderate temperature.  What they found is summarized in this graph from their paper, which shows that people from larger cities walk significantly faster.  There was a threefold difference between the smallest and largest towns!

Their interpretation, which they based on the work of psychologist Stanley Milgram, was a bit dicey: they suggested that larger towns overload the mental processing ability of their inhabitants, and so the people simply walk faster in bigger towns “to minimize environmental stimulation.”  There are, of course, other interpretations—I’m sure you can think of a few.  (Rushing to and from work over larger distances is one.)

Regardless, this was one of those crazy but appealing ideas that we scientists get sometimes, and testing it did point to something interesting.  I’m sure, though, that these results would no longer be publishable in Nature.

This is by way of introducing another crazy idea I had a while back, and have been chewing over for some time.  It’s also about “the pace of life,” but about the pace of our entire lives.  If you’ve lived a substantial time, as I have, you may have noticed that the seasons and years seem to be passing more quickly than when you were younger.  This summer, for instance, seems to me to have vanished in a flash.  And I’ve noticed this more strongly as I’ve gotten older.

So I made a hypothesis: one sees the passage of time in relation to the length of one’s past life.  The duration of each moment is weighed in relation to how many moments have gone before, and so seems more fleeting when you’ve experienced more moments.  And that’s why, for older people, time seems to pass more quickly.  An alternative hypothesis is that as one gets closer to the close of one’s life, one senses “time’s wingèd chariot” more prominently, so time seems to pass more quickly because you don’t have as much left.  (I call this the Raitt Hypothesis after Bonnie Raitt’s song, “Nick of Time,” which includes this lyric: “Life gets mighty precious when there’s less of it to waste.”)

Both of these theories, however, predict that as one gets older, one’s perception of time becomes compressed.

I realize that this is just a dumb idea, but it’s eminently testable. Here’s my experiment:  take a number of people of different ages, put them in a room, and ask them to tell you when an hour has passed.  Of course, you can’t let them count (that’s why I suggest an hour rather than a minute), and perhaps there should be some distraction so that people are doing quotidian tasks when asked to judge the time elapsed.  My hypothesis would predict that older people would  think that an hour had gone by after a shorter time than younger people; in other words, there would be a negative correlation between age and actual time elapsed.

I’m not aware that anyone has done such an experiment, though it’s an obvious idea, and maybe the notion is flawed, but surely a significant correlation (either positive or negative) would mean something.  If anything has been published on it—because, of course, I’ll never actually do this experiment—let me know.

Does this sound totally off the wall?

Just to round out this post, here’s an apposite song from 1966:  “Time,” by the Pozo Seco singers. It was their only hit, but it was popular in the U.S.  If you remember this, you’re old enough to have noticed how time seems to be passing faster.