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 Birds of America Audubon. Due in part to the Civil War, the edition was never finished; only 15 parts of the 44 part series were completed. This edition consisted of 105 plates and included none of the original text. Fewer than 100 subscriptions were sold, making this edition rarer than other early editions. Audubon's practice of obtaining his subjects has been described as:“Audubon used what we like to call today as the barrel-of-the-shotgun method...After he killed the birds, he would use a complex system of wires and strings to position the birds. Previous artists would draw the birds in a stiff position, but