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? *2 points a. 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. b. barve found an association between habitat temperature and feather structure among himalayan songbirds, lending new support to a general prediction. c. barve discovered that songbirds have adapted to their environment by growing feathers without flat and smooth sections, complicating an earlier hypothesis. d. 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 A: The text says biologists predicted feather structure - temperature relation, and Barve's study (on 249 songbird species in Himalayas) found high - elevation species have more downy feathers (for insulation) and longer feathers. There's no mention of "better regulate body temperature than other species" or "contradicting previous predictions", so A is wrong.
2. Analyze Option B: Biologists predicted feather structures vary with habitat temperature. Barve studied 249 songbird species in different Himalayan elevations (different temperatures) and found feather structure differences (more downy, longer in high - elevation). This means he found an association between habitat temperature and feather structure, supporting the general prediction. This matches the text.
3. Analyze Option C: The text has no information about "growing feathers without flat and smooth sections" or "complicating an earlier hypothesis", so C is incorrect.
4. Analyze Option D: There's no "Landor’s established belief" mentioned in the text related to this study, so D is wrong.

Answer:

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