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 Clements Checklist of Birds of the World is the official list used by the American Birding Association for birds globally. eBird also uses the "Clements" checklist as the base list for its eBird taxonomy, which in addition to species includes hybrids and other non-species entities reported by birders. The Clements Checklist of Birds of the World The Clements Checklist of Birds of the World is a book by Jim Clements which presents a list of the bird species of the world. The most recent printed version is the sixth edition (2007), which was published by Cornell University Press. Previous editions were published by the author's own imprint,