Category Archives: birds

Avian Scavengers

A number of birds will scavenge animal remains of all sorts. The most obvious are vultures but also several birds of prey including eagles, crows and even smaller birds such as roadrunners and Jays. This is an important ecological service to clean up what could otherwise be a source of disease. Actually some of the scavenging birds not specially adapted to the lifestyle can become ill from eating carrion.

Some scavenging birds, including our national symbol the bald eagle, are on occasion poisoned with lead bullet fragments in gut piles left over from field-dressed deer. A couple of lead fragments the size of a grain of rice can be lethal to an eagle.

The most commonly encountered scavengers are the Black and Turkey Vultures frequently seen cleaning up road-killed armadillos, possums, skunks, etc. They share some features and are distinct in others. They are both dark birds with bald heads. The lack of a feathered pate was thought to be for hygiene but recently its been suggested to be for thermoregulation. They also share incredibly acidic stomachs. The gastric juices of the Turkey Vulture are more acidic than a car battery and nearly one hundred times as acidic as our stomachs.

Vultures literally turn down their temperature at night by several degrees. In the morning they can be seen with their wings spread wide to the sun. Another method of temperature regulation involves urohidrosis, defecating down their legs in hot weather. This provides some cooling and may also be beneficial in the management of bacteria on their legs.

If approached by a predator or human for that matter they vomit. Some authors suggest this is a defensive action, as their vomitus is so acidic that it can cause burns. Other authors disagree, but all agree that the loss of the vomitus lightens the body weight to aid take-off for escape. Neither variety of vulture has a syrinx so they can only make grunting or hissing noises.

Black Vultures are slightly smaller than the Turkey Vulture. They have a poor sense of smell, therefore they detect a meal via keen eyesight. They will frequently soar higher than other vultures and follow them to a carcass. Black Vultures can show up in large numbers during the birth of livestock. Not only will they consume the afterbirth but also attack and kill newborn animals, and hence can constitute a serious agricultural pest.

Turkey Vultures are slightly larger and have a distinctive red head. Also, they have a somewhat brownish tinge to their feathers when viewed up close. They have the keenest sense of smell among birds. They tend to soar somewhat closer to the ground sniffing constantly for the odor of a carcass.

The importance of vultures was highlighted in India and Pakistan a decade ago. When the vulture population crashed due to the presence of a toxic (to vultures) arthritis drug in cattle carcasses, stray/feral dogs stepped up to fill the niche as scavengers. The dog population rapidly increased as did rabies. It caused a spike in human deaths due to rabies from dog bites.

Dr. Bob Allen, Ph.D., is Emeritus Professor of Chemistry at Arkansas Tech University.

A Few Red Birds

T his summer the color of Bullfrog Valley is red, for birds anyway. There are the eponymous Cardinals who literally define their color – Cardinal red. They are year round residents and very common visitors at bird feeders. Cardinals are all red, save a black face and are distinguished by a tuffed head.

North America’s only all red bird is the Summer Tanager, and a summer visitor to the area. The male as noted is all red, sort of a strawberry color while the female is an olive yellow color. They aren’t often seen at feeders because they are insectivores grabbing large numbers of bees and wasps from the air. They are common but not often seen. They are best detected nearby from their sound. They have a distinct call note that sounds like a downward pitched “tsk, tsk, tsk, tsk.”” Also denoted as pit-ti-tuck.”

The Scarlet tanager also spends it summers here. The male is red the female yellowish green, is hard to find in the canopy and is insectivorous. The only difference is this red tanager has black wings. The distinct call note for the Scarlet Tanager is “chick-burrr.”

One more somewhat red bird, now a year round resident, is the house finch. They fill the day at my feeders eating lots and lots of sunflower seed. They are a predominately brown/tan finch, but the males have a red head, throat, and rump.

So much for a little natural history of a few local red birds, now the why and how of red birds. The why is clear. The brighter the color the better, due to it’s signaling fitness to a mate. One of the ways a female measures the health of a possible mate may be via the the proxy of bright colors. It’s true of not only red but any other bright color or combination thereof.

There seem to be a whole complement of genes that “travel” together evolutionarily speaking. Genes that lead to bright colors, or striking patterns, or big antlers for that matter seem to be linked with genes the contribute to fitness. These would be genes for physical or ever immunologic strength, genes for adaptability, or even intelligence. This evolutionary cooperativity has been referred to as a society of genes.

So bright redness is indicative of fitness, the fitter birds succeeding in the game of evolution. Now how about the how? How do bird make or get these bright colors? It’s all in the biochemistry. It turns out that birds redness comes from a birds ability to convert dietary components which contain pale yellow pigments. Bright red birds have an excess of a particular enzyme know as cytochrome P450, an enzyme shared with animals and used mainly to detoxify certain toxins. It also converts pale yellow pigments to bright red pigments.

In a study of red vs yellow domestic canaries, the red variety had thousands of times the cytochrome P450 activity as their yellow conspecifics. The pale yellow pigments are converted to bright red pigments, then deposited in feathers and voila, bright red birds.