Homing pigeons can be taken from their lofts and transported hundreds

Homing pigeons can be taken from their lofts and
transported hundreds of kilometers in covered cages to
unfamiliar sites and yet, when released, be able to
choose fairly accurate homeward bearings within a
(5) minute and fly home. Aside from reading the minds of
the experimenters (a possibility that has not escaped
investigation), there are two basic explanations for the
remarkable ability of pigeons to “home”: the birds
might keep track of their outward displacement (the
(10) system of many short-range species such as
honeybees); or they might have some sense, known as
a “map sense,” that would permit them to construct an
internal image of their environment and then “place”
themselves with respect to home on some internalized
(15) coordinate system.

The first alternative seems unlikely. One possible
model for such an inertial system might involve an
internal magnetic compass to measure the directional
leg of each journey. Birds transported to the release site
(20) wearing magnets or otherwise subjected to an
artificial magnetic field, however, are only
occasionally affected. Alternately, if pigeons measure
their displacement by consciously keeping track of the
direction and degree of acceleration and deceleration of
(25) the various turns, and timing the individual legs of the
journey, simply transporting them in the dark, with
constant rotations, or under complete anesthesia ought
to impair or eliminate their ability to orient. These
treatments, however, have no effect. Unfortunately, no
(30) one has yet performed the crucial experiment of
transporting pigeons in total darkness, anesthetized,
rotating, and with the magnetic field reversed all at the
same time.

The other alternative, that pigeons have a “map
(35) sense,” seems more promising, yet the nature of this
sense remains mysterious. Papi has posited that the
map sense is olfactory: that birds come to associate
odors borne on the wind with the direction in which the
wind is blowing, and so slowly build up an olfactory
(40) map of their surroundings. When transported to the
release site, then, they only have to sniff the air en
route and/or at the site to know the direction of home.
Papi conducted a series of experiments showing that
pigeons whose nostrils have been plugged are poorly
(45) oriented at release and home slowly.

One problem with the hypothesis is that Schmidt-
Koenig and Phillips failed to detect any ability in
pigeons to distinguish natural air (presumably laden
with olfactory map information) from pure, filtered air.
(50) Papi’s experimental results, moreover, admit of
simpler, nonolfactory explanations. It seems likely that
the behavior of nostril-plugged birds results from the
distracting and traumatic nature of the experiment.
When nasal tubes are used to bypass the olfactory
(55) chamber but allow for comfortable breathing, no
disorientation is evident. Likewise, when the olfactory
epithelium is sprayed with anesthetic to block smell
detection but not breathing, orientation is normal.

1. Which one of the following best states the main idea of the passage?

(A) The ability of pigeons to locate and return to their homes from distant points is unlike that of any other species.
(B) It is likely that some map sense accounts for the homing ability of pigeons, but the nature of that sense has not been satisfactorily identified.
(C) The majority of experiments on the homing ability of pigeons have been marked by design flaws.
(D) The mechanisms underlying the homing ability of pigeons can best be identified through a combination of laboratory research and field experimentation.
(E) The homing ability of pigeons is most likely based on a system similar to that used by many short-range species.


2. According to the passage, which one of the following is ordinarily true regarding how homing pigeons “home”?

(A) Each time they are released at a specific site they fly home by the same route.
(B) When they are released they take only a short time to orient themselves before selecting their route home.
(C) Each time they are released at a specific site they take a shorter amount of time to orient themselves before flying home.
(D) They travel fairly long distances in seemingly random patterns before finally deciding on a route home.
(E) Upon release they travel briefly in the direction opposite to the one they eventually choose.


3. Which one of the following experiments would best test the “possibility” referred to in line 6?

(A) an experiment in which the handlers who transported, released, and otherwise came into contact with homing pigeons released at an unfamiliar site were unaware of the location of the pigeons’ home
(B) an experiment in which the handlers who transported, released, and otherwise came into contact with homing pigeons released at an unfamiliar site were asked not to display any affection toward the pigeons
(C) an experiment in which the handlers who transported, released, and otherwise came into contact with homing pigeons released at an unfamiliar site were asked not to speak to each other throughout the release process
(D) an experiment in which all the homing pigeons released at an unfamiliar site had been raised and fed by individual researchers rather than by teams of handlers
(E) an experiment in which all the homing pigeons released at an unfamiliar site were exposed to a wide variety of unfamiliar sights and sounds


4. Information in the passage supports which one of the following statements regarding the “first alternative” (line 16) for explaining the ability of pigeons to “home”?

(A) It has been conclusively ruled out by the results of numerous experiments.
(B) It seems unlikely because there are no theoretical models that could explain how pigeons track displacement.
(C) It has not, to date, been supported by experimental data, but neither has it been definitively ruled out.
(D) It seems unlikely in theory, but recent experimental results show that it may in fact be correct.
(E) It is not a useful theory because of the difficulty in designing experiments by which it might be tested.


5. The author refers to “the system of many short-range species such as honeybees” (lines 9–11) most probably in order to

(A) emphasize the universality of the ability to home
(B) suggest that a particular explanation of pigeons’ homing ability is worthy of consideration
(C) discredit one of the less convincing theories regarding the homing ability of pigeons
(D) criticize the techniques utilized by scientists investigating the nature of pigeons’ homing ability
(E) illustrate why a proposed explanation of pigeons’ homing ability is correct


6. Which one of the following, if true, would most weaken Papi’s theory regarding homing pigeons’ homing ability?

(A) Even pigeons that have been raised in several different lofts in a variety of territories can find their way to their current home when released in unfamiliar territory.
(B) Pigeons whose sense of smell has been partially blocked find their way home more slowly than do pigeons whose sense of smell has not been affected.
(C) Even pigeons that have been raised in the same loft frequently take different routes home when released in unfamiliar territory.
(D) Even pigeons that have been transported well beyond the range of the odors detectable in their home territories can find their way home.
(E) Pigeons’ sense of smell is no more acute than that of other birds who do not have the ability to “home.”


7. Given the information in the passage, it is most likely that Papi and the author of the passage would both agree with which one of the following statements regarding the homing ability of pigeons?

(A) The map sense of pigeons is most probably related to their olfactory sense.
(B) The mechanism regulating the homing ability of pigeons is most probably similar to that utilized by honeybees.
(C) The homing ability of pigeons is most probably based on a map sense.
(D) The experiments conducted by Papi himself have provided the most valuable evidence yet collected regarding the homing ability of pigeons.
(E) The experiments conducted by Schmidt-Koenig and Phillips have not substantially lessened the probability that Papi’s own theory is correct.