Design of the Month

Bird navigation

The following quotation is taken from page 18 of the New Scientist of 31 October 2009.

Birds that navigate using the Earths' magnetic field rely more on their eyes than on the magnetic particles in their nostrils, an experiment on robins suggests.

Rival theories of bird navigation have suggested both mechanisms. Now Henrik Mouritsen, at the University of Oldenburg, Germany, and his team have show[n] that eyes could be key. In one group of robins, the team removed cluster N, a brain region involved in processing signals from the “pair-forming photopigments” in the eyes thought to relay magnetic compass information. In another group, the team cut the trigeminal nerve, which sends siganls to the brain from the magnetic particles in the nostrils.

The researchers then exposed the surgically treated and untreated robins to the Earth's natural magnetic field, and also to a field which artificially rotated magnetic north 120 degrees anticlockwise. The robins lacking their nostril-to-brain connection weren't tricked, locating the true and artificial magnetic norths just as well as the controls. But the robins without cluster N were unable to navigate. “The results raise the distinct possibility that this part of the visual system enables birds to ‘see’ magnetic compass information,” conclude the researchers (Nature, DOI: 10.1038/nature08528).

  1. What were the experimental units?
  2. What were the treatments and how many of them were there?
  3. Assuming that 36 robins were used, and that all treatments were equally replicated, construct the skeleton analysis of variance table.
  4. How do you think the experiment was designed and randomized?
  5. Can you improve on the design or the randomization?
  6. If you have access, read the letter in Nature and then answer the questions again.

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