LIFE IN THE FAST LANE
Birds live at a pace that would leave us breathless, exhausted, and starving. How do they keep up the pace? Like high-speed jets, birds have special features to use fuel (food and oxygen) fast and efficiently. Their fast-paced lifestyle (rapid metabolism) depends on efficient lungs, a large, fast-beating heart, and a rapid digestive system.
Lungs exchange oxygen and carbon dioxide between the blood and air. Bird lungs are smaller than those of mammals, yet they are part of the most efficient respiratory machinery known in vertebrates. Even with this efficient respiratory system, birds breathe rapidly during flight - up to 450 breaths per minute for a pigeon.
Unique to birds are air sacs. Air sacs act as a bellows to suck air into the body, then circulate it in a one-way flow through the lungs - giving the lungs a constant flow of fresh air.
The nine air sacs also act as a cooling system since birds do not have sweat glands. They contribute to stability in flight by lowering the center of gravity and act as shock-absorbers in diving birds, such as Brown Pelicans. During courtship, male grouse inflate special air sacs on their chests like brightly colored balloons to attract a mate.
A bird's heart is much like yours - a four chambered muscle that pumps blood throughout the body. A bird's heart weighs up to twice as much as that of a mammal of equal size because flying is strenuous. Energy-hungry muscles need a bigger, faster beating heart to send them plenty of oxygen and nutrients.
Smaller birds and mammals lead fast-paced lifestyles and generally have faster heart rates than large ones.
Hummingbird 600 beats per minute at rest Pigeon 200 beats per minute at rest Ostrich 65 beats per minute at rest Human 70 beats per minute at rest
For an animal to use food as fuel, it must digest the food - break it down small enough to be absorbed into the bloodstream - and get rid of the waste products. A bird's gut looks much like your own, but there are some differences. Many seed and grain-eating birds have a crop connected to the esophagus. The expandable crop allows birds to quickly gather and store a large amount of food, then retreat to safety to digest it.
A bird has two stomachs (we have one) to digest its food in record time. In four hours, a Spur-winged Goose can digest the same meal that it takes a rabbit 24 hours to digest. In the upper stomach, the proventriculus, food is broken down with digestive enzymes.
The lower stomach, the ventriculus, or gizzard, is a tough, muscular organ which crushes and grinds up the food, just like our teeth do for us. Remember a bird has no teeth, so it swallows food whole. Birds that eat plants and seeds have more powerful gizzards than meat and fish eaters. Many birds swallow grit or gravel to help the gizzard break down food.
Birds are known for their fast reactions, balance, coordination and instinctive behavior. Bird brains are relatively larger than those of reptiles but smaller than those of mammals. Birds are not known for reasoning abilities however, some birds do have significant learning abilities, such as parrots trained to talk or do tricks.