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Alive & KickingThe Adaptation of Birds |
Today I saw a Great Blue Heron in a large cow pasture. I was reminded of a student's preparation of such a skeleton in one of my classes.
He prepared the skeleton using a common museum technique employing Dermestid beetles, which rather quickly strip the soft tissues from the bones. The bones are then scrubbed clean with Boraxo soap solution and bleached with a bleach solution.
He mounted the standing skeleton with the aid of fine wire and a wood dowel. It was a beauty:
I was amazed at its lightness. Fully equipped, the four-foot-tall bird - musculature, feathers and all - weighed about seven pounds full-grown.
All animals are smart in their own way of life, even the "lowly" earthworm - nature requires it for survival.
Birds, especially, are wonderful examples of specialization.
One has only to look at the adaptation of their structure to see how birds have changed to meet life's requirements.
Excess weight is seldom found in flying birds. For example, they have no teeth but eat small stones to grind their food and then dump the rocks. Aft er quick growth, the feathers become hollow and light.
Females have one ovary, not two.
Their major bones are hollow and air-cooled.
Young birds are not born as in mammals (imagine a pregnant bird coming in for a landing carrying a dozen half-developed eggsinstant omelet!) Carrying waste makes no sense at all: a bird's digestive tract is short, with mere minutes between "scoop and poop."
A bird's temperature ranges between 108 degrees and 112 degrees F, depending on the species and their activities. (Such body temperatures in humans would result in rapid death.) This elevated temperature supports the rapid metabolism needed to support sustained flight. If you have watched ducks fly, you know something of their energy demand. A hummingbird's heart is oft en 1/5 its body weight; its beats have been counted at 1000 per minute.
Birds have the most exceptional vision in the animal kingdom. If a human could see as well as a hawk, newsprint could be read at 100 yards. Vultures can successfully scan for food at over 5,000 feet above the earth.
Since birds' eyes are usually located on the sides of their heads, they can see 3-D only directly ahead and behind them; but by turning their agile necks, the 360-degree 3-D vision can quickly be brought to focus where needed. It's a marvel to watch a Sharp-shinned Hawk (Acipitor) fly through thick brush at 30 miles per hour, dodging branches in pursuit of its winged prey. Three-dimensional vision and excellent eye-wing coordination are required. Birds, also, have exceptional hearing ability. Experiments with barn owls in total darkness have determined they can locate mice by sound alone.
Birds' feet show great specialization. Consider the many woodpeckers, which have two forward and two backward toes on each foot to help grasp tree bark while in search of food. Webbed feet are found on many swimmers and divers. Three forward toes and one backward toe are found on those birds like the Robin and common chicken, used to scratch the earth in search of food. The tearing talons on an eagle are specialized tools that play an important part in their survival.
Perching birds' feet lock to their perch when they squat to sleep: a tendon pulls the toes when the leg is bent, causing them to clamp to the perch.
Even feathers are specialized into three types. Down feathers preserve heat; contour feathers give the body and wings their aerodynamic shape; and flight feathers function in navigation control and propulsion.
Unlike hair, feathers overlap and, when oiled, keep the bird dry. Ducks and geese keep their outboard motors (feet) in the water while floating warm and dry above.
But what about cold feet?
Nature has put very few sensory nerve endings in a water bird's feet. In the leg, arteries containing warm blood destined for the feet lie against the veins that return blood from the feet. This architectural detail conserves heat energy by transferring the heat of the arterial blood into the cool, veinous blood returning from the feet.
This is conservation of energy at its best, an adaptation to save heat energy from being lost to the cold lakes of Minnesota.
All living animals and plants are beautifully specialized to cope with their own unique survival problems. Over the passing of eons, they appear to adapt well to environmental changes. It is the ecological catastrophe rapidly presented and in many cases provided by man's activities to which they cannot safely adapt.
Guest columnist John Cooke taught high school biology for 30 years and is pleased to share his insights with our readers.