Final answer:
The category that includes birds, mammals, and reptiles is vertebrates, as they all share the common characteristic of having a backbone.
Step-by-step explanation:
The category that includes all others in the list—birds, mammals, reptiles—is vertebrates. Vertebrates are animals with a backbone, which is a primary feature that includes a diverse group of animals such as mammals, birds, reptiles, amphibians, and fish. The vertebral column, or backbone, is essential for protecting the spinal cord and distinguishes vertebrates from invertebrates, which lack this structure. Examples of vertebrates include species as varied as bats, whales, crocodiles, and sparrows, all sharing the common trait of having a vertebral column.