GRE Reading Comprehension: JiJing 352-GRE阅读机经352篇 - Y90TIS0FOW0768T4K

Orcas are small whales that generally travel in groups called pods. Orcas that feed on marine mammals travel in very small pods, while those that feed on fish travel in relatively large pods. Since a larger pod has an increased collective ability to locate prey, it is likely that orcas that feed on mammals travel in small pods only because the mammals that they hunt can more easily detect a large pod and escape it.