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 kind of dance to flush out the aquatic inhabitants. Skimmers have different-sized mandibles, the lower one being used to skim the water's surface for small fish. Ducks have developed an assortment of angling skills. Some dabble, like the mallard, while others are of a more streamlined design and are at home underwater, such as the merganser. Waders, which specialise in feeding on mud flats at low tide, include avocets, godwits, dowitchers and sanderlings. The pelican feeds in groups, their pouch-like bills being more successful when used collectively. Boobies fish in the open ocean and are shown dive-bombing shoals "en masse".