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
Birds of the Amazon birds that breed in the northern and southern hemisphere but migrate to the Amazon rainforest for food and shelter that are not available at their breeding places during cold months. Migrating birds greatly rely on rainforests for food, rest and recovery after their dangerous migration during which they can lose 30% of their body weight. Since the 1970s, cattle pasture has been the leading cause of deforestation in the Brazilian Amazon. Land is often cleared for investment purposes due to pastureland prices exceeding forest land prices. In this case, large amounts of forest are torn down and replaced with savanna