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
Mail pouch a mail pouch is mail sealed against postal inspection. An example of first-class mail is a typed letter or one written by hand. It must weigh less than 13 ounces. Registered mail that would be carried in a mail pouch is mail that is within a certain length and width, regardless of thickness. Registered mail can be insured up to $25,000 for a certain premium fee. There is no limit on the value of an item sent in by registered mail. Registered mail is closely guarded and given maximum security like in handling with a locked mail pouch. Military mail