Question

biologists have predicted that birds’ feather structures vary with habitat temperature, but this hadn’t been tested in mountain environments. ornithologist sahas barve studied feathers from 249 songbird species inhabiting different elevations—and thus experiencing different temperatures—in the himalaya mountains. he found that feathers of high-elevation species not only have a greater proportion of warming downy sections to flat and smooth sections than do feathers of low-elevation species, but high-elevation species’ feathers also tend to be longer, providing a thicker layer of insulation. which choice best states the main idea of the text?
barve’s investigation shows that some species of himalayan songbirds have evolved feathers that better regulate body temperature than do the feathers of other species, contradicting previous predictions.
barve found an association between habitat temperature and feather structure among himalayan songbirds, lending new support to a general prediction.
barve discovered that songbirds have adapted to their environment by growing feathers without flat and smooth sections, complicating an earlier hypothesis.
the results of barve’s study suggest that the ability of birds to withstand cold temperatures is determined more strongly by feather length than feather structure, challenging an established belief.

Explanation:

1. Analyze Option 1: The text says biologists predicted the feather - temperature relationship, and Barve's study tested it in mountain environments (supported, not contradicted). So this option is wrong.
2. Analyze Option 2: Biologists predicted feather structures vary with habitat temperature. Barve studied Himalayan songbirds at different elevations (different temperatures) and found feather structure differences related to elevation (temperature). This supports the general prediction with new mountain - environment data. This matches the main idea.
3. Analyze Option 3: The text says high - elevation species have a greater proportion of downy to flat/smooth sections, not no flat/smooth sections. Also, it supported the prediction, not complicated a hypothesis. So this option is wrong.
4. Analyze Option 4: The text shows both feather structure (proportion of downy) and length matter for insulation, and there's no claim that length is more important than structure, nor that it challenges a belief. So this option is wrong.

Answer:

B. Barve found an association between habitat temperature and feather structure among Himalayan songbirds, lending new support to a general prediction.