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
An Annotated Checklist of the Birds of the Oriental Region a discussion of the rationale behind the choice of English names, the systematic list (195 pages), a 17-page references list containing 814 items, and indexes of both English and scientific names. There is also a map of the region covered (supplementing the textual description within the introduction), and a list of eight excluded species. Works which used this work for their taxonomic basis include: Reviews of the checklist can be found in the following: An Annotated Checklist of the Birds of the Oriental Region An Annotated Checklist of the Birds of the Oriental Region is a 1996 softback book published