South Carolina READY 4th Grade Science Practice Test

Birds are defined as feathered vertebrates, which means they are animals that have feathers and possess a backbone. Feathers are a distinctive characteristic unique to birds and are crucial for various functions, such as flight, insulation, and display. Vertebrates are animals that have a spinal column, which includes not only birds but also mammals, reptiles, amphibians, and fish.

The other options do not accurately capture the defining characteristics of birds. For example, while some birds may swim or live in trees, not all species fit those descriptions. Additionally, birds are not mammals, and the notion that they are “mammals that can fly” is incorrect as birds and mammals belong to different classes of animals within the animal kingdom. Thus, the definition that includes being feathered vertebrates best describes what encompasses birds.