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 Danube Delta territory. As far as the habitats are concerned, the species of the aquatic ones almost exclusivity feed from the aquatic millennium, while those living in the terrestrial habitat hardly have 50 per cent terrestrial food, the remainder having a mixed and aquatic origin. Many species owe their presence or existence in the delta – in rather high densities as compared to the rest of the area – just to this food richness. The contrast created between the great food abundance available as compared to the existence for some species of plenty of sites for nest location resulted in the simple