BIRDS: A SPECIAL CREATION

Picture of Birds Flying

adapted from an article by

Jacques Foucher

Used with the kind permission of the Creation Science Movement, 50 Brecon Avenue, Cosham, Portsmouth, England, P06 2AW.

Most zoologists who support the doctrine of evolution believe that birds came from reptiles. This conclusion is based largely on the fossil evidence of a few skeletal similarities between birds and certain dinosaur species and the fact that at least some species of dinosaurs laid eggs. Little attention is paid to soft-tissue comparisons because skin, internal organs, etc. are hardly ever preserved in the fossil record. Still, differences in the form and function of organs relating to circulation, digestion, respiration, communication, and so on can be just as important as skeletal differences in taxonomy.

Birds are remarkably well suited to their airborne way of life. Only the combined effect of many special characteristics makes flight possible for them. Given the number of these unique features, it seems very unlikely that the aves could have evolved piecemeal from a lowly reptilian ancestor into the some 9,000 species of aerial acrobats we see today. Let us look at just a few of the anatomical characteristics of birds to see why.

The Bones

The bones of reptiles, like those of mammals, are filled with marrow. But the bones of birds are a combination of hollow, trussed tubes (see Figure 1) and thin, curved plates, making their bones light yet strong. Air-filled bones not only has save weight, but connections to the respiratory system allow extra oxygen to be available for meeting the demands of extreme muscle exertion during flight.

The sternum in birds is relatively deep compared to the reptilian sternum, enabling it to function as a keel to anchor the strong flight muscles and support the wings by the strut-like coracoid bones (see Figure 2). This specialized sternum ensures the bird is efficiently suspended by its wings during flight.

Figure 1: Bone Structure

Body Temperature

Birds are warm-blooded creatures, and their normal body temperature of 40?C to 43?C (104?F to 110?F) is high in comparison with other animals. Because chemical processes are accelerated at higher temperatures, the metabolic rhythm of the bird is relatively fast, especially compared to the cold-blooded reptiles, whose body temperatures and metabolic rates depend on environmental factors.

Figure2: The Sternum Keel

Put another way, the bird lives a far more intense existence than the reptile - appropriate for a creature that regularly “defies” gravity, travels at high speed and, in its smaller varieties, negotiates a tangle of leaves and branches unscathed.

The Circulatory System

In stark contrast to the limited mobility characterizing the life of most reptiles, birds are highly active creatures. When not walking or hopping about, they are often knifing through the air. Flight involves intense muscle effort, particularly on take off. Even level flight can be demanding when traveling at the robin's 30 to 50 koph (20 to 30mph), the 50 to 65 kph (30 to 40 mph) of starlings and mourning doves, or the speedy 65 to 100 kph (40 to 60 mph) of geese, ducks, and swifts. To attain these high levels of performance, birds need very rapid blood circulation. Therefore, the avian heart is comparatively heavy, and it beats faster, as well. At rest, the heart of the house sparrow beats 460 times a minute. Compare this to the reptilian heart rate: the heart rate of one type of skink (the Tiliqua), for example, ranges from a mere 20 bpm (beats per minute) at 20?C to a maximum of 121 bpm at 40?C. When especially burdened, the heart rate of a bird can double, allowing the circulatory system to take full advantage of the exceptional efficiency of the avian lung.

The Digestive System

Most birds have a digestive system that includes a crop, a special holding device something like a pocket. Food goes into the crop whole. From there, it passes into the stomach (the proventriculus and the gizzard), where digestion begins. Therefore, birds have no need to rest in order to masticate or digest their food.

They can take full advantage of their extraordinary ability to cover a large territory in search of food. On migration, they can gorge themselves on a stopover to store up energy for the next leg of their journey. The rapid metabolism of birds ensures that all food can be quickly processed to meet the energy of the flight muscles.

The Respiration System

Birds have an amazing unidirectional respiratory system. Air entering through the windpipe (trachea) passes directly into air sacs located towards the rear of the bird. From there, the oxygen-laden air travels forward through the lungs and a system of air sacs toward the front of the body, where it is finally exhaled. Tubes connecting the bird's air cavities to the lungs permit air to travel in just one direction through the lungs. Thus, birds do not share the reptilian (and mammalian) experience of an ebb and flow of oxygen supply: avian bodies receive a constant supply of oxygen. Moreover, the capillaries in the lungs of birds are exceptionally thin, enabling the exchange of gases to be extremely rapid. These features, along with other specialized anatomical attributes, allow birds to achieve and maintain the high level of muscle performance necessary for flight.

The air sacs of birds (see Figure 3) are unique in the animal world. It was once supposed these sacs - usually nine in number - served only to make birds lightweight, but it is now known they are an integral part of the respiratory system and they are the principal means of venting the life-threatening heat generated by the intense muscle activity of flight.

Figure 3: Air Sacs

Moreover, the sacs assist waterfowl in diving, serve as shock absorbers on landing for some of the heavier birds, are essential to avian vocalizations, and have display functions in the mating rituals of birds such as the grouse.

Communication

Yet another anatomical feature found only in birds is the syrinx (derived from the Greek word for piping; reed, cane, and clay panpipes having been used to make music in ancient times). It is what birds use to produce their songs (territorial vocalizations) and calls (vocalizations for mating, warning of danger, etc.). The syrinx consists of a flexible membrane stretched over a cartilaginous frame set at the bottom of the trachea, forming a kind of air sac at the junction of the two bronchi. This often melodic means of avian communication, so essential to their survival and reproductive success, is not even hinted at in the reptiles.

Feathers

Combining strength with lightness of weight, feathers are among the most beautiful creations and the natural world. Each bird sports between 1,000 and 25,000 contour, semi-plume, down, filoplume, and bristle feathers (see Figure 4).

Contour feathers are what most of us think of when we think of feathers. They serve as the outer covering of the body of the bird and the flight feathers. Each feather is made up of a central midrib (rachis) to which is attached a series of tight, parallel barbs (see Figure 5). Each barb has tiny barbules, which have hooks to keep them linked with neighbouring barbules.

Figure 4: Feathers Types
Figure 5: Contour Feather Design

The feather “coat” is waterproofed and kept supple by a specially formulated oil secreted from a gland at the base of the tail. Birds spread this oil over their feathers using their beaks in the act known as preening.

Another type of feather with which most people are familiar is down. Down feathers lack the barbs found on contour feathers and so have a more open, fluffy appearance. In winter, a thick, heavy layer of down is produced under the body contour feathers of northern birds. Down makes excellent insulation, enabling hardy species to survive the cold winter weather. Many birds have the good sense to pluck their down and line their nests with it to help keep their eggs warm in the spring.

Looking like an intermediate between contour and down feathers, semi-plumes provide additional insulation and also fill out the bird, giving it an aerodynamic shape. Tiny filoplumes have free nerve endings, which are connected to receptors around the follicle. They likely serve to keep contour feathers in place during preening, display, and flight. Bristle feathers, with few if any barbs, have localized purposes, such as forming the eyelashes.

The childish but common speculation that feathers evolved from “frayed reptilian scales” remains unsupported by scientific evidence. The structural complexity of feathers defies the simplistic, evolutionary explanation of their origin.

Hearing and Sight

Hearing and sight are keen in birds, exceptionally so in some species. Birds can detect sounds that are inaudible to us, and it is among birds that we can find the best sight in all the animal kingdom. An eagle can discern its prey upon the ground from altitudes that make the eagle itself invisible to our unaided eye.

Small birds dart to and fro under the cover of trees without ever brushing against branches or leaves. Their ability to adjust their visual focal length virtually instantaneously is essential, given the speed with which they move through the air.

The Feet

The feet of each kind of bird are exactly right for the purposes they serve, such as perching, hopping, running, grasping, scratching, or paddling. The bone structure of the birds foot is simple: the lower leg and foot our bones fused to sustain the punishment of repeatedly landings. Unlike reptiles, which have muscles throughout their limbs and feet, even the toe flexor muscles of perching birds are located above the “knee.” The leg tendons lie in narrow tubes surrounded by a circulating liquid, permitting very rapid motion (see Figure 6). The tendons pass in front of the knee, behind the “heel,” and run beneath the toes. As the bird bends its legs when lighting on a branch, the tendons automatically tighten and clamp the feet to the branch.

Figure 6: The Perching Mechanism

The bird will not become dislodged without first voluntarily straightening its legs. This is why birds do not fall off their perches when they are asleep.

Conclusion

We cannot know everything about fossilized creatures when we have only their bones to examine. But having looked at just a few of the remarkable traits of avian anatomy, we may well ask: What sort of intermediate yet functional form can one imagine between a reptilian scale and a birds feather, or the bellows-like action of reptilian lungs and the continuous, one-way flow of air in birds, or between toes having independent muscles and the tendon-controlled feet of birds? None. And what of the complex changes in the nervous system, reproductive system, behaviour patterns, and so on that would have to accompany a transformation from the generally slow-paced, restricted, earth-bound life of reptiles to the fast-paced, well-travelled, airborne life of most birds? If any one of the anatomical components of a bird were not fully formed and functioning perfectly, and supported by complementary changes in the workings of the brain and the behaviour it produces, the mutant would not survive long enough to reproduce.

If animals are specially designed creations, it should not be surprising to find some biological mechanisms shared across taxonomic divisions. It is as if the Designer was picking and choosing from a vast array of biological systems when putting His creations together. The eye of the octopus is very like that of man, yet no one alleges that man evolved from octopi - or vice versa. Birds lay eggs because it is a viable way for them to bear young; there is no need to infer an evolutionary relationship to reptiles. And a few crude skeletal similarities between birds and selected reptiles speaks of a common design strategy for dealing with similar structural requirements of a particular part of the body - evolutionary connections are not necessary.

We need to acknowledge that the Creator is a supremely intelligent Being working out His purpose. Birds were made to fly and that is why they have so many uniquely appropriate features. As 1 Corinthians 15:39 says, “All flesh is not the same flesh: but there is one kind of flesh of men, another flesh of beasts, another of fishes, and another of birds (emphasis added).

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