Bird anatomy Birds have a four-chambered heart, in common with mammals, and some reptiles (mainly the crocodilia). This adaptation allows for an efficient nutrient and oxygen transport throughout the body, providing birds with energy to fly and maintain high levels of activity. A ruby-throated hummingbird's heart beats up to 1200 times per minute (about 20 beats per second). Many birds possess a muscular pouch along the esophagus called a crop. The crop functions to both soften food and regulate its flow through the system by storing it temporarily. The size and shape of the crop is quite variable among the birds. Members
Human uses of birds down are used for bedding, insulation, and other purposes. Birds were among the wild animals hunted for food before the Neolithic revolution and the development of agriculture. For example, in the Epipaleolithic of the Levant, between c. 14,500 and 11,500 BP, both waterfowl and migratory birds were eaten. Archaeologists have studied the return in terms of energy from captured food compared to the energy expended to capture it; birds provide a smaller return than larger game such as deer, but better than many plant materials. For example, waterfowl captured in a drive can yield a return of around 2,000 kcal/hour,