The Red Notebook

Charles Darwin was a great experimenter. In his later life at Down House, he conducted scores of weird and wonderful experiments on pigeons, fowl, plants, seeds, dogs, his own children, you name it; he would experiment on it. But he also found time to conduct some experiments during the Beagle voyage. He even got to perform an experiment on that most iconic of South American birds, the condor.

Condor, Canyon del Colca, Peru (cc gudi&cris)

Darwin describes his condor experiment in The Voyage of the Beagle. He gets off to what would nowadays be thought of as a pretty bad start:

April 27th. … This day I shot a condor. It measured from tip to tip of the wings, eight and a half feet, and from beak to tail, four feet.

He then describes the range and habits of condors before getting on to his experiment on some live, captive condors:

Remembering the experiments of M. Audubon, on the little smelling powers of carrion-hawks, I tried […] the following experiment: the condors were tied, each by a rope, in a long row at the bottom of a wall; and having folded up a piece of meat in white paper, I walked backwards and forwards, carrying it in my hand at the distance of about three yards from them, but no notice whatever was taken. I then threw it on the ground, within one yard of an old male bird; he looked at it for a moment with attention, but then regarded it no more. With a stick I pushed it closer and closer, until at last he touched it with his beak; the paper was then instantly torn off with fury, and at the same moment, every bird in the long row began struggling and flapping its wings. Under the same circumstances, it would have been quite impossible to have deceived a dog.

…a classic blind test—although it seems strange to use the phrase when experimenting on the sense of smell.

Darwin goes on to observe:

The evidence in favour of and against the acute smelling powers of carrion-vultures is singularly balanced. Professor Owen has demonstrated that the olfactory nerves of the turkey-buzzard (Cathartes aura) are highly developed, and on the evening when Mr. Owen’s paper was read at the Zoological Society, it was mentioned by a gentleman that he had seen the carrion-hawks in the West Indies on two occasions collect on the roof of a house, when a corpse had become offensive from not having been buried, in this case, the intelligence could hardly have been acquired by sight. On the other hand, besides the experiments of Audubon and that one by myself, Mr. Bachman has tried in the United States many varied plans, showing that neither the turkey-buzzard (the species dissected by Professor Owen) nor the gallinazo find their food by smell. He covered portions of highly-offensive offal with a thin canvas cloth, and strewed pieces of meat on it: these the carrion-vultures ate up, and then remained quietly standing, with their beaks within the eighth of an inch of the putrid mass, without discovering it. A small rent was made in the canvas, and the offal was immediately discovered; the canvas was replaced by a fresh piece, and meat again put on it, and was again devoured by the vultures without their discovering the hidden mass on which they were trampling. These facts are attested by the signatures of six gentlemen, besides that of Mr. Bachman.

The degree to which certain birds use smell to detect food is still a controversial topic. Most birds seem to have a poor sense of smell, but others such as kiwis and certain sea birds do seem to make use of it while foraging/hunting for food. Although turkey vultures seem to have a good sense of smell, experiments have shown that it does not appear sufficiently acute to detect odours from high altitude.

167 years after Darwin performed his condor experiment, the controversy continues.

As I was driving up the hill towards my house this evening, a sparrowhawk took off from a telegraph pole and flew down the road in front of me for about 100m. I had a great view of it, and clocked it at a leisurely 22mph.

OK, so not one of the most useful measurements ever taken in the history of science, but data nevertheless.

See also

• Hunting the hunter
• Sparrowhawk
• My sparrowhawk photos

Charles Darwin carried out some pretty weird experiments in his time. The dead pigeon stuffed full of seeds floating in salt water, that was one of his. So was searching for seeds in the mud on ducks’ feet. But the experiment that really took the biscuit was the one in which he played music to worms. As he explains in the first chapter of The Formation of Vegetable Mould through the Action of Worms:

Worms do not possess any sense of hearing. They took not the least notice of the shrill notes from a metal whistle, which was repeatedly sounded near them; nor did they of the deepest and loudest tones of a bassoon. They were indifferent to shouts, if care was taken that the breath did not strike them. When placed on a table close to the keys of a piano, which was played as loudly as possible, they remained perfectly quiet.

Playing a bassoon to earthworms eighty years before anyone ever heard the name Monty Python: Charles Darwin was years ahead of his time.

Indeed he was. Imagine my delight yesterday, reading an article in New Scientist [subscribers only link] describing a number of modern-day experiments which involved playing music to animals. Here’s my favourite:

Ava Chase of the Rowland Institute at Harvard in Cambridge, Massachusetts, has shown that carp can tell the difference between baroque music and John Lee Hooker, depressing a button with their snouts to indicate which is which (Animal Learning & Behavior, vol 29, p 336).

Playing baroque music and the blues to carp. Darwin (and Python) would have been delighted.

But doesn’t Ms Chase realise that fish prefer sole music?

Note: The Rowland Institute website has a page about Ava Chase’s fish laboratory, which contains links to videos of her carp experiments, and a copy of her paper Music discriminations by carp (Cyprinus carpio) [PDF].

[Note (14-Feb-2008): I received a number of comments on the following post. Within the comments, I speculated that the New Scientist article cited below might have confused seconds with milliseconds. One of the co-authors of the paper mentioned by New Scientist confirmed that the magazine had got it wrong, but that there should actually have been no units. This invalidates much of my original criticism of their experiment, although I remain sceptical. Please check out the comments for more details. The comments did not survive a relocation of this blog.]

New Scientist: Monkeys tune in to your way of thinking (subscribers only)

… Vittorio Gallese of the University of Parma, Italy, has found that macaques can predict the future actions of others, casting doubt on the long-held idea that monkeys cannot understand other beings as agents with their own perspectives and intentions.

Six macaque monkeys were shown a simple goal-related task – a woman reaching over a tall obstacle to pick up a toy resting on the other side. Once the monkeys had got used to this, the obstacle was removed so that the woman could simply reach out and pick up the toy.

The team found that when she did this, the monkeys showed a minimal amount of interest in her actions: each gazed at her face for an average of just 7 milliseconds. If, however, she continued to behave as if the obstacle were still in place and used the “reach-over” path to the toy, the monkeys showed more interest, gazing at her face for around 18 milliseconds on average (Current Biology, DOI: 10.1016/j.cub.2007.12.021).

Gallese concludes that the results show that monkeys recognise intention in goal-related tasks, and use that ability to predict how others will act. When no obstacle was in place but the woman still reached for the toy as if it were, she was acting in an unexpected manner, and Gallese says the monkeys spent longer gazing at her face because they were looking for clues to explain her behaviour.

Let’s put these timings into perspective. The difference between 7 milliseconds and 18 milliseconds is just over 1/100th of a second. A typical television set displays pictures at 30 frames per second (i.e. each frame appears to last for 33 milliseconds—or about twice as long as these monkeys gawp in astonishment at the woman’s unexpected behaviour). Blink, and you would literally miss it.

In what way can looking at something for 18 milliseconds be described as a gaze? Gallese seems to be reading an awful lot into such fleeting glances.

Note: The following duplicates an item I have just published on my other website. But as it describes a fun, scientific experiment involving physics and biology, I thought it also belonged in the Red Notebook.

This week, I finally managed to carry out a little experiment I’ve been planning for some time. The delay was because I needed access to a military jet-fighter.

You must have noticed how, when a jet-fighter flies past, the noise it makes appears to come from behind the aircraft. When I was a kid, I mistakenly believed that this was because the jet was flying faster than the speed of sound. The real reason is that the light arriving at your eyes from the jet is travelling at approximately 300,000,000 metres per second, whereas the sound arriving at your ears from the jet is travelling at around 330 metres per second—roughly a million times slower. This means that the light arrives at your eyes pretty much instantaneously, whereas the sound arrives at your ears slightly later, depending on the distance of the jet. By the time the sound arrives, the jet has moved several fusilage lengths further along its flightpath, meaning that you are seeing the jet where it is now, but you are hearing the jet where it was a short while ago.

We are able to judge the direction from which a sound is coming because we have two ears. When the sound is coming from the right, say, it arrives at our right ear a split second before it arrives at our left. It is also, thanks to the inverse-square law of acoustic waves, and to the fact that our ears point in opposite directions, louder in our right ear than our left. Our brains use these differences and other subtle cues to calculate the direction of the sound. Amazing, or what?

I finally got to perform my experiment on Monday evening. I was in the garden watering my tomatoes when I spotted a jet-fighter travelling down the valley towards me, low and fast. Its flightpath would take it about 100 metres in front of where I was standing. So I dropped the watering can and hurried to a location on the patio with a better view.

As the jet flew past, the sound appeared to be coming from a few plane-lengths behind the aircraft. Then I took out my other piece of vital experimental apparatus—my right index finger—and inserted it firmly into my right ear. As if by magic, the sound from the jet suddenly appeared to be coming directly from the aircraft. Unable to detect the direction of the sound with data from only one ear, my brain quite sensibly deduced that it must be coming from the plane.

For the remaining few seconds that the jet was in view, I repeatedly removed from and inserted into my ear my index finger, causing the direction of the sound to move repeatedly back and forth.

Give it a go some time. You don’t really need a jet-fighter; any noisy, fast-moving aircraft will do.

• The man who mistook his hat for a telescope
• Transit
• Experiment