The Habitat Directs Animal Adaptations

by Dave Hanks

How does a species survive when it’s too hot, too cold, too wet or too dry? Over a period of years, the individuals that can stand the conditions better survive. Because it’s difficult to reproduce when one is dead, those with the best survival traits do the reproducing. Gradually the resulting offspring become adapted to withstand the existing environmental conditions. Behavior is also an adaptation. (i.e. shade seeking to get out of the sun, seeking cover to get away from a cold wind, or trying to blend in with one’s surroundings, are some examples).

TOO HOT: Longer, slimmer appendages that allow the blood to be closer to the surface to expel heat, and fat deposits in one spot to avoid covering the body which prevents heat loss. Humps on camels and fat tails on desert sheep are prime examples.

TOO COLD: Just opposite of too hot. These animals have short limbs, thick bodies, with their fat distributed evenly over their bodies. They are usually bigger (i.e. Alaska Moose are larger than Idaho Moose) which lowers the percent of surface area in relation to size and preserves body warmth.

TOO DRY: These have a very interesting adaptation to satisfy their water needs – they make their own from the carbohydrates they eat. A carbohydrate molecule is simply 6 molecules of water with 6 carbon atoms attached. Kick the carbon atoms off the molecule and you have water. We humans do the same, but get rid of the water, which is necessary to get rid of other waste products and cleanse our systems. Hot climate animals have to have devised other means of cleansing their systems

TOO WET: These animals develop sleek, steam lined bodies, appendages for movement in water, and counter shading (Dark on dorsal surface and light underneath on their ventral areas – camouflage from both above and below).

The Greater Yellowlegs (Pictured) is a bird of THE WET. Notice its white belly and dark, mottled top. It’s well camouflaged.

Bird Life is a Hazardous Life!

A bird’s life is fraught with problems. Of those individuals that are mature enough to migrate in the fall, only about a third of them are alive to return to their breeding grounds in the spring. But before that, young birds have tremendous obstacles to survive before they can be included in the fall migration numbers.

Around 60% of altricial (helpless) young born in open nests will hatch. One third of these will fledge. Cavity nesters have a better chance at life because the young are better protected and more mature before leaving the nest hole. About 75% will hatch and a little less than half will fledge. The period between leaving the nest, learning to feed oneself, and full flight is extremely perilous.

Precocial birds usually nest on the ground and only a third to a half of their eggs will reach hatching. Even though precocial chicks can run and feed themselves, they require parental protection. Many water bird young will be carried on their parent’s backs or under the adult’s wings.

The SONG SPARROW (pictured) is a generalist that will nest on the ground, in trees or in bushes. However, they do prefer brushy or marshy areas, even though they will nest in farming areas, along roadsides, and even in suburbia. This common bird can be recognized by its streaked breast and a large dot in the middle of its chest. It is a singer that lives up to its name. Two thirds of Song Sparrow eggs hatch, half will fledge, but 80% will die before their first year is up, and only 10% will make it back to their breeding grounds.

Because bird life is so hazardous, heavy reproduction is necessary to maintain each species, as survival odds are not in their favor!

A Song Sparrow bursting with song