[Martin Taylor 2010.10.11.11.10]
(Actually a few minutes earlier than the time stamp. but I liked the string)
Someone apparently did a test for a controlled variable with bower birds.
I haven't looked at the original paper, which requires purchase or a subscription. Here's a link to the abstract <http://www.cell.com/current-biology/abstract/S0960-9822(10)01036-5>, and the description of the study in Science (Random Samples, 17 Sept 2010 p1449):
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The twiggy structures Australia's male great bowerbirds build to attract mates are impressive, adorned with shells, rocks, and bones. Now research suggests that the embellishments may allow the males to appear larger than they really are.
Called avenues, the structures are courting areas for male bowerbirds. Researchers suspected that the decorations' placement was aimed at females but didn't know why. So biologists mapped the positions of thousands of objects in front of 33 male bowerbirds' avenues. The decorations were placed by size, from small to large, with the smallest items closest to the entrance. When a female enters the avenue, she sees a male at the far end. The objects' arrangement may make the male look "larger and more conspicuous" from the female's vantage point, says Natalie Doerr, an evolutionary biologist at the University of California, Santa Barbara, and co-author of the study, published online 9 September in Current Biology.
When the researchers rearranged the designs, the males put them back in the original order. This behaviour suggests the birds are making deliberate choices, possibly implying some kind of cognitive talent, says Irene Pepperberg, a comparative psychologist at Harvard University. "It's a great study, with valuable new insights about the birds' visual processing," she says.
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If the Science description is correct, which I can't tell from the journal abstract, the researchers tested whether the birds were controlling the size gradient of the approach to the bower, whether or not they knew that's what they were doing. The birds did seem to correct a disturbance to that gradient. To human eyes, a large-to-small gradient would indeed make the bird at the end of the bower seem bigger. Whatever the effect on the females, reorganization over evolutionary time appears to have made controlling this variable enhance the male's mating success. I don't know whether physically larger bowerbirds have greater mating success, which would be something one would want to know before putting too much credence on what Pepperberg or Doerr claim the study demonstrates. What are the females controlling for when they choose a partner?
As an aside, Pepperberg was the owner (?) of the grey parrot Alex, who seemed to understand and to be able to answer verbally some kinds of questions about the environment, such as "How many blue" or "What colour square" when confronted with a tray full of objects variously coloured and shaped, and of a variety of materials. In one TV show about Alex, it was said that when Alex was perched on Pepperberg's shoulder while she was teaching another parrot to talk, Alex piped up "Speak more clearly"! Alex was said to act as though he was jealous of Pepperberg's male students. but not of her female ones. It's hard to know which of these things are really true, but it's fun to think they might be. If so, and Pepperberg had a lot of exprience with Alex and other birds, it's not unreasonable for her to think in terms of "cognitive talent".
What do you call a genetically developed perceptual control system such as what the bowerbirds seem to have? Surely to control a size gradient in the layout of objects collected from the environment is perceptual control, and the layout gradient is not an intrinsic variable. The control of the layout gradient must influence an intrinisic variable, a variable related to mating, but the effect on this variable is created only through its effect on female behaviour. This presumably means either that it disturbs some controlled perception in the female or that it provides an environmental affordance whereby the female can control some perception that is not at its reference value. Presumably that control itself influences some intrinsic variable in the female associated with mating: mating with a larger male brings that variable nearer its reference than mating with a smaller male would do?
However you slice it, we seem to be dealing with social control, by which I mean controlling some perception so that its side effects or direct effects influence the actions of another.
Martin