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 to mimic speech. Among reasons for their popularity is that they can be kept in homes too small or otherwise unsuitable for dogs or cats. The cagebird trade in some parts of the world threatens certain species with extinction, when birds are illegally captured in the wild. For example, in Indonesia, at least 13 species are close to extinction including the Indonesian national bird, the Javan hawk-eagle, while five subspecies including the scarlet-breasted lorikeet may have become extinct in the wild. Pet birds are kept in their millions, as are domestic fowls, bantams, and pigeons. These last had an important