Monthly Archives: February 2020

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.

Feedback Accelerates Global Warming

Positive feedback to global warming keeps climate scientists up at night. Feedback can accelerate the rate of change in the climate. The worst-case scenario involves tipping points where the heating of the air and water make parts of the planet uninhabitable.

A frightening irony concerning global warming is the use of air conditioning to combat the heat. We obviously don’t think about cooling our homes and offices right now, but that is part of our problem. Using air conditioning requires power to generate the necessary electricity. The electricity comes to a large degree from burning fossil fuels which contribute to global warming. This short term reaction to a meteorologic phenomenon contributes to a long term climatological phenomenon.

Climate scientists call this positive feedback. Burning fossil fuels to run air conditioners contributes carbon dioxide to the atmosphere which traps heat and makes the planet warmer, which requires more air conditioning, which causes carbon dioxide release which causes more heating which… You get the picture.

In this case, the feedback has a human element. Other feedback loops are purely physical phenomena. These feedback loops add to the complexity of climate modeling. Predictions of future climate rely on computer calculations, the accuracy of which depends on how well the variables in a climate system are understood.

Water vapor in the atmosphere is without question the most important of the global warming feedback loops. Water vapor is a strong greenhouse gas itself; that is, its presence in the atmosphere traps heat and contributes to global warming. The positive feedback comes about because the amount of water vapor in the atmosphere is directly proportional to the temperature of the atmosphere. The hotter the atmosphere the more water vapor, the more water vapor in the atmosphere, the more heat trapped in the atmosphere, the more water vapor in the atmosphere, the more… you get the picture.

When natural gas (methane) is burned it produces carbon dioxide, a major greenhouse gas. Unburned methane released to the atmosphere is itself a potent greenhouse gas. There are vast stores of methane trapped in the permafrost of the tundra and the continental shelf under the oceans. As the planet warms, the permafrost thaws which releases methane. Methane release warms the planet thawing more permafrost which releases more methane which… you get the picture.

The amount of solar heating of the planet is a function of the albedo, the reflectivity of the planet. Sunlight is strongly reflected by snow-covered expanses near the north and south poles. As the climate warms due to global warming, the snow melts exposing soil which is much less reflective.

The less reflective soil traps more heat, warming the planet further, melting more snow, which traps more heat… you get the picture

The same is true of sea ice and the oceans. Ice is more reflective than water. As the ice cover melts, more heat is trapped, as more heat is trapped more ice melts… you get the picture.

A final irony is that as the area of the oceans covered with ice shrinks, it opens more area to exploration and untimely production of crude oil. Burning these fossil fuels adds more carbon to the atmosphere, which warms the planet… I hope you get the picture.

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