Reading comp PrepTest 104 · Section 3 · Question 16

Topic: Science

Paragraph 1

• Paragraph note
  • Homing pigeons’ ability to find their way home is probably due to either an ability to keep track of outward displacement or an internal map sense.
• Views, minor Meta-Structures, and the author's attitude
  • Phenomenon: Homing pigeons can be transported in covered cages hundreds of kilometers to unfamiliar places and, upon release, determine accurate homeward bearings within one minute (first sentence)
  • Experimentation has ruled out the possibility that pigeons read the minds of experimenters (second sentence)
  • Explanations:
    • Pigeons keep track of outward displacement like short-range species such as honeybees (second sentence)
    • They have an internal map sense that allows them to locate themselves on a coordinate system (second sentence)
  • Author’s attitude: “and yet” (first sentence); “remarkable ability” (second sentence); “might keep track” (second sentence); “might have some sense” (second sentence)

Paragraph 2

• Paragraph note
  • Assessment of explanation 1: It is unlikely that homing pigeons are able to keep track of outward displacement.
• Views, minor Meta-Structures, and the author's attitude
  • Possible model for keeping track of displacement: internal magnetic compass (second sentence)
    • This has been largely disproved by experiments in which birds were subjected to artificial magnetic fields but were only occasionally affected (third sentence)
  • Another possible model for keeping track of displacement: track direction and degree of acceleration and deceleration of turns, and timing of individual legs of journey (fourth sentence)
    • This has been largely disproved by experiments in which birds were transported in dark, with constant rotations, or under anesthesia (fourth-fifth sentences)
    • No one has combined the countermeasures in all of these experiments into one experiment (sixth sentence); so this possibility has not totally been ruled out
  • Author’s attitude: “seems unlikely” (first sentence); “might involve” (second sentence); “only occasionally affected” (third sentence); “ought to impair or eliminate” (fourth sentence); “have no effect” (fifth sentence); “unfortunately, no one has performed the crucial experiment” (sixth sentence)

Paragraph 3

• Paragraph note
  • Assessment of explanation 2: possibility that pigeons have an internal map sense seems more plausible, but it has not been proven.
• Views, minor Meta-Structures, and the author's attitude
  • Unclear what form this internal “map sense” takes (first sentence)
  • Papi’s theory: internal map is olfactory; pigeons come to associate wind-blown smells from different directions with different areas (second sentence)
    • Experimentation at first seems to support this, because pigeons whose nostrils are plugged find their way home slowly (fourth sentence)
  • Author’s attitude: “seems more promising” (first sentence); “remains mysterious” (first sentence); “Papi has posited” (second sentence); “have only to sniff the air” (third sentence); “Papi conducted” (fourth sentence)

Paragraph 4

• Paragraph note
  • Papi’s olfactory explanation has been weakened by experimentation.
• Views, minor Meta-Structures, and the author's attitude
  • Schmidt-Koenig and Phillips’s experiment: pigeons didn’t distinguish natural, signal-laden air from filtered air (first sentence)
  • Papi’s results could be explained in other ways (second sentence):
    • It was the trauma of the nostril-plugging that caused pigeons’ slow navigation, not the fact that they couldn’t smell (third sentence)
    • Another experiment: when nasal tubes are used to allow for comfortable breathing but no smelling, pigeons behave normally (fourth sentence); and when anesthetic is used to block smell sense but not breathing, pigeons behave normally (fifth sentence)
  • Author’s attitude: “one problem” (first sentence); “failed to detect” (first sentence); “admit of simpler, nonolfactory explanations” (second sentence); “it seems likely” (third sentence); “distracting and traumatic” (third sentence); “no disorientation is evident” (fourth sentence)

Main Point: Two explanations have been proposed for the remarkable ability of homing pigeons to find their way home: the first, which posits that the birds keep track of external displacement, seems to be less likely than the second, which posits that the birds are able to locate themselves on an internal coordinate system that has not yet been characterized.

Paragraph 1, Sentence 1 (P1 S1) - Statement of phenomenon

P1 S2 - Two explanations

P2 S1 - First explanation unlikely

P3 S1 - Second explanation more likely, but still mysterious

Phenomenon/Explanation: This passage uses a Phenomenon/Explanation Meta-Structure. The phenomenon to be explained is stated in the first sentence: the amazing ability of homing pigeons to be transported hundreds of kilometers in covered cages to unfamiliar places and set a course for home within a minute of being released. Two possible explanations are proposed, namely, the possibility that the birds keep track of their route from home on the outward journey, and that the birds have an internal coordinate system that they use to navigate. The author argues that the second has more support than the first, but concedes that the nature of the internal map system has yet to be determined, though it has been shown by experimentation that it is unlikely to be olfactory.

The minor Meta-Structure is List. The author lists two possible explanations for the phenomenon and then, for each explanation, lists the experiments that have been performed in order to test it.

The author’s viewpoint is not difficult to discern throughout the passage. They favor the second explanation over the first, and are interested in finding out the nature of the pigeons’ internal map sense. In fact, they spend the second half of the passage recounting the experiments that have been done to try to figure this out.

This passage is straightforward in terms of what it’s discussing and what the author’s perspective is, but, as with many science passages that discuss experimentation, the author does not declare a definitive explanation of the phenomenon; the reader is left with probabilities. However, the evidence is well organized.