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
Cheek pouch face with food." When full, the pouches can make the hamsters' heads double, or even triple in size. The platypus feeds on annelid worms, insect larvae, freshwater shrimps, and yabbies (freshwater crayfish) that it digs out of the riverbed with its snout or catches while swimming. It uses its cheek-pouches to carry prey to the surface for eating. The cheek pouch is a specific morphological feature that is evident in particular subgroups of rodents (i.e. Heteromyidae and Geomyidae (or Gopher)), yet a common misconception is that certain families, like Muridae (including the common black and brown rats), contain this structure