Many birds that form flocks compete through aggressive interaction for

Many birds that form flocks compete through
aggressive interaction for priority of access to
resources such as food and shelter. The result of
repeated interactions between flock members is that
(5) each bird gains a particular social status related to its
fighting ability, with priority of access to resources
increasing with higher status. As the number and
intensity of interactions between birds increase,
however, so increase the costs to each birds in terms of
(10) energy expenditure, time, and risk of injury. Thus,
birds possessing attributes that reduce the number of
costly interactions in which they must be involved,
without leading to a reduction in status, are at an
advantage. An external signal, such as a plumage type,
(15) announcing fighting ability and thereby obviating the
actual need to fight, could be one such attribute.

The zoologist Rohwer assented that plumage
variations in Harris sparrows support the status
signaling hypothesis (SSH). He reported that almost
(20) without exception birds with darker throats win
conflicts with individuals having lighter plumage. He
claimed that even among birds of the same age and sex
the amount of dark plumage predicts relative
dominance status.

(25) However, Rohwers data do not support his
assertions: in one of his studies darker birds won only
57 out of 75 conflicts; within another, focusing on
conflicts between birds of the same age group or sex,
darker birds won 63 and lost 62. There are indications
(30) that plumage probably does signal broad age-related
differences in status among Harris sparrows: adults,
usually dark throated, have higher status than juveniles,
who are usually light throated; moreover, juveniles
dyed to resemble adults are dominant over undyed
(35) juveniles. However, the Harris sparrows age-related
plumage differences do not signal the status of
individual birds within an age class, and thus cannot
properly be included under the term status signaling.

The best evidence for status signaling is from the
(40) greater titmouse. Experiments show a strong
correlation between the width of the black breast
plumage stripe and status as measured by success in
aggressive interactions. An analysis of factors likely to
be associated with breast-stripe width (sex, age, wing
(45) length, body weight) has demonstrated social status to
be the only variable that correlates with stripe width
when the other variables are held constant.

An ingenious experiment provided further evidence
for status signaling in the greater titmouse. One of
(50) three stuffed titmouse dummies was mounted on a
feeding tray. When a live bird approached, the dummy
was turned by radio control to face the bird and present
its breast stripe in display. When presented with a
dummy having a narrower breast stripe than their own,
(55) birds approached closely and behaved aggressively.
However, when presented with a dummy having a
broader breast stripe than their own, live birds acted
submissive and did not approach.

1. According to the passage, the status signaling hypothesis holds that the ability to display a recognizable external signal would have the effect on an individual bird of

(A) enabling it to attract a mate of high status
(B) allowing it to avoid costly aggressive interactions
(C) decreasing its access to limited resources
(D) making it less attractive to predatory species
(E) increasing its fighting ability



2. The author refers to the fact that adult Harris sparrows are usually dark throated (lines 31-32), in order to do which one of the following?

(A) support the conclusion that plumage variation among Harris sparrows probably does not signal individual status
(B) argue that plumage variation among Harris sparrows helps to confirm the status signaling hypothesis
(C) indicate that in light of plumage variation patterns among Harris sparrows, the status signaling hypothesis should probably be modified
(D) demonstrate that Harris sparrows are the most appropriate subjects for the study of status signaling among birds
(E) suggest that the signaling of age-related differences in status is widespread among birds that form flocks



3. Which one of the following, if true, would most seriously undermine the validity of the results of the experiment discussed in the last paragraph?

(A) The live birds all came from different titmouse flocks.
(B) The physical characteristics of the stuffed dummies varied in ways other than just breast-stripe width.
(C) No live juvenile birds were included in the experiment.
(D) The food placed in the feeding tray was not the kind of food normally eaten by titmice in the wild.
(E) Even the live birds that acted aggressively did not actually physically attack the stuffed dummies.



4. Which one of the following best describes the organization of the passage?

(A) A hypothesis is introduced and studies relevant to the hypothesis are discussed and evaluated.
(B) A natural phenomenon is presented and several explanations for the phenomenon are examined in detail.
(C) Behavior is described, possible underlying causes for the behavior are reported and the likelihood of each cause is assessed.
(D) A scientific conundrum is explained and the history of the issue is recounted.
(E) A scientific theory is outlined and opinions for and against its validity as well as experiments supporting each side are compared.



5. According to the passage, which one of the following is true of Rohwers relationship to the status signaling hypothesis (SSH)?

(A) Although his research was designed to test the SSH, his data proved to be more relevant to other issues.
(B) He set out to confirm the SSH, but ended up revising it.
(C) He set out to disprove the SSH, but ended up accepting it.
(D) He altered the SSH by expanding it to encompass various types of signals.
(E) He advocated the SSH, but his research data failed to confirm it.



6. The passage suggests that among birds that form flocks, a bird of high status is most likely to have which one of the following?

(A) dark throat plumage
(B) greater-than-average body weight
(C) offspring of high status
(D) strong fighting ability
(E) frequent injuries



7. Which one of the following can be inferred about Harris sparrows from the passage?

(A) Among Harris sparrows, plumage differences signal individual status only within age groups.
(B) Among Harris sparrows, adults have priority of access to food over juveniles.
(C) Among Harris sparrows, juveniles with relatively dark plumage have status equal to that of adults with relatively light plumage.
(D) Juvenile Harris sparrows engage in aggressive interaction more frequently than do adult Harris sparrows.
(E) Harris sparrows engage in aggressive interaction less frequently than do greater titmice.