Paragraph Summaries
- Birds that form flocks are relatively better off if they win fights, but fights also are costly. A bird will have the best of both worlds if it can demonstrate fighting ability without actually fighting. Feathers could show fighting ability, for example.
- In “Harris sparrows”, dark feathers predict fighting ability.
- However, dark feathers also increase with age. Dark feathers predict adults as a groups will win fights, but the feathers can’t predict how individual birds will do.
- In the “greater titmouse”, the width of a certain stripe does predict social status, and therefore fighting ability.
- An experiment confirmed that the greater titmouse sees a larger breast stripe as a status signal.
Analysis
The structure of this passage is a bit more complex than usual.
The first paragraph describes the effect of status, and introduces a hypothesis: birds might be able to maintain high status and yet avoid fights by showing certain feathers.
A hypothesis is not certain. It needs to be proven. So the author tells us about two studies.
Rowen’s study tries to prove the hypothesis, but it fails. In Harris sparrows, dark throats seem to be a sign of adulthood, not status.
The second study does help prove the theory. Titmice behaved aggressively or submissively depending on whether the fake titmouse had a large or small stripe.
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