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
The Life of Birds only other species, but also cameras, a car alarm and a chain saw. Broadcast 2 December 1998, this programme discusses mating rituals. If a male bird is on the lookout for a partner and has a suitable nest, it must advertise the fact, either by its call, a visual display or both. The frigatebird provides an example of the latter, with its inflated throat pouch. The hornbill's courtship, among that of many others, also runs to the offer of a gift. For some species, dancing can also be an important component, and grebes are shown performing a "pas de deux".