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 An interesting ethologic aspect appearing enhanced by the conditions of the Danube Delta (especially by the floods) is represented by egg laying in common nests. Thus, as a consequence of the general lack of egg-laying places, especially at flood time when a great part of the aquatic-species nests are flooded, the birds this way affected go on laying eggs in alien nests either belonging to the same species or to species of the same families. The following up of the tropic regime of the deltaic birds according to its origin had in view to know the food cycles, especially as