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 final production represented by birds, the classification of these latter in categories with aquatic, mixed and respectively terrestrial nutritive regimes. In this respect, the delta birds appear as having a trophic regime of predominantly aquatic origin owing to the huge quantity the nutritive biomass of this milieu is produced in the Danube Delta in the warm season of the year. While the sedentary species generally close their trophic chains at the delta's level, the migratory, the passage, and the wintertime species annually carry away from the Danube Delta a great part of the nutritive biomass accumulated while resting in this