Self-study
P1
Many birds that form flocks compete through aggressive interaction for priority of access to resources such as food and shelter. ███ ██████ ██ ████████ ████████████ ███████ █████ ███████ ██ ████ ████ ████ █████ █ ██████████ ██████ ██████ ███████ ██ ███ ████████ ████████ ████ ████████ ██ ██████ ██ █████████ ██████████ ████ ██████ ███████ ███
Phenomenon ·
Status hierarchy in birds
Top bird has best fighting ability which grants them first dibs on food and shelter. Then next bird get their turn, then next, and so on. Each bird has a position on this status hierarchy.
Negative Consequence ·
Maintaining social status is costly: energy, time, and risk of injury
Hypothesis ·
Status signaling hypothesis (SSH)
Instead of actually fighting to establish social status, birds can instead signal their fighting ability and thereby not have to risk actually getting hurt. A bird's plumage is one such signal of fighting ability.
P2
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Rohwer ·
Sparrow plumage supports SSH
Birds with darker throats win conflicts against birds with lighter plumage, controlling for age and sex.
P3
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Critique of Rohwer ·
Data doesn't support his claims
Darker plumage birds don't always win conflicts. Also, age is actually a confounder. Age is a signal of status and plumage just happens to darken with age. Hence, plumage is not a status signal for these sparrows.
P4
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Experimental Evidence for SSH ·
Greater titmouse
Width of black breast-plumage stripe signals status. Experiment controlled for sex, age, wing length, and body weight.
P5
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Experimental Evidence for SSH ·
Greater titmouse
Stuffed titmouse dummies with narrower v. broader breast stripes caused other birds to behave aggressively v. submissively, as predicted by SSH.
Passage Style
Critique or debate
Phenomenon-hypothesis (RC)
20.
The passage suggests that among █████ ████ ████ ███████ █ ████ ██ ████ ██████ ██ ████ ██████ ██ ████ █████ ███ ██ ███ ██████████
a
dark throat plumage
The passage doesn’t suggest that this is typical of birds of high status among birds that form flocks. Dark plumage is related specifically to Harris sparrows. But we don’t know that dark plumage is possessed by other kinds of birds that form flocks.
b
greater-than-average body weight
This isn’t mentioned as something possessed by birds of high status.
c
offspring of high ██████
This isn’t mentioned as something possessed by birds of high status.
d
strong fighting ability
e
frequent injuries
This isn’t mentioned as something possessed by birds of high status.