Birds must accomplish the same internal processes as all other vertebrates— digesting and absorbing food, bringing oxygen and nutrients to the cells, eliminating carbon dioxide and other wastes, and responding to their environment. The challenge is accommodating these diverse tasks in a lightweight flying package. Each of the familiar life processes discussed in this section is uniquely modified by the Creator to serve a bird’s high-energy lifestyle.
Digestion in Birds
- High body temperature and flying means they have an enormous energy demand.
- So they eat large quantities of food.
- Some adult birds can eat a quarter of their weight in a day
- Once ingested, the food is quickly digested.
- This is essential because birds cannot afford to carry heavy quantities of food in their stomachs.
- Uses its unique beak for gathering food.
- Appearance and use vary with the bird’s diet.
- Food is usually swallowed whole, passes through the esophagus and enters the crop.
- Crop is a holding area for the food.
- From the crop, it passes into the first part of the stomach (proventriculus) where digestion juices are produced.
- The gizzard is the second part. Here the food is ground down by sand and stones that the bird swallows.
- The food then passes into the intestine, where final digestion and absorption occurs.
- Undigested wastes are passed into the cloaca and then out of the body.
- The cloaca is a common opening for the intestines, kidney ducts, and reproductive organs.
Respiration
- Their lungs are unable to provide enough oxygen.
- A series of air sacs aids the lungs.
- 25% of the air is draw in the lungs & 75% to the air sacs.
- As the bird exhales, the air in the lungs passes out, and the fresh air from the air sacs passes through the lungs.
- Fresh air passes through the lungs during inhaling and exhaling.
- Respiration also helps them remain cool.
- They sweat a little, but not enough.
- They pant like dogs.
- Also used for vocalization.
- They have a syrinx (song box).
- They perfect the call by imitating others from their species.
Circulation and Excretion
- 4 chambered heart
- What does this mean?
- Complete separation of oxygenated and deoxygenated blood.
- Right side of heart receives the blood and pumps it to the lungs.
- Lungs oxygenates the blood which then goes to the left side of the heart.
- From there it is pumped to the body.
- To maintain their high metabolism, the heart beats rapidly. Average of 135-570 bpm. Some species can reach 1000 bmp.
- Birds generally don’t die of old age, but “burn themselves out.”
- They have high blood pressure and can die of heart failure in times of stress.
- Metabolic wastes are filtered from the blood by a pair of kidneys.
- Waste empties directly into the cloaca.
- No bladder. Makes them lighter for flight.
Response
God’s design becomes more obvious from a study of the various animals. Reptiles, amphibians, and fish rely heavily on the senses of smell and taste. In contrast, their vision and hearing are weak. Many of these animals live in a watery environment that muffles sound and reduces light, making hearing and vision of little value. Even those reptiles and amphibians living on land have little use for strong eyes; they live in or close to the ground, limiting their field of vision. God provided the specific senses these animals need for their activities and environment.
- Birds have large, generally immovable eyes. Birds must move their neck to look around.
- Some birds have better eye sight than us.
- A hawk can spot a rabbit from 1.5 km away.
- Owls can spot prey in 1/10 to 1/100 of the brightness needed for man to see.
- Birds have ear canals covered by feathers.
- They have sensitive hearing in the upper sound range.
- The brain of the bird is larger than all other vertebrates except mammals.
- Olfactory lobes are small, smell is not important (except for birds that feed on dead animals.
- The cerebrum, responsible for instinct, is also large.
- Optic lobes are large.
- Cerebellum, coordinates the muscular activities, is large.
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