let me describe A mysterious bird that vividly illustrates some of the biological challenges birds have had to overcome to live as long as they do.
My mystery bird is tiny and weighs about the same as a US penny. When active, it requires so much energy that it needs to eat several times its own body weight in food every day just to keep from starving. During flight, its wings beat 80 times per second, and every gram of its flight muscles produces up to 10 times the energy of a top human athlete’s muscles when both are working at maximum capacity. In fact, it has the highest metabolic rate of any endothermic animal—and it is very endothermic. Its typical body temperature of 40°C (104°F) would be a dangerously high human fever. It needs so much fuel to keep up this energy expenditure that when it is inactive it lowers its body temperature to that of its surroundings in order not to starve in its sleep. His heart is beating at a machine gun-like 20 beats per second. Even at rest, he breathes 250 times a minute, about as fast as a panting dog, to get enough oxygen. After all, if he were human, his normal blood sugar level would make him a dangerous diabetic.
How long do you think it lives?
I was just describing a hummingbird—specifically, a ruby-throated hummingbird (Archilochus colubris), the species commonly hopping around parks and gardens in the eastern United States. Hummingbirds fuel their frenetic lifestyles by sucking nectar—a rich mixture of sugars—from flowers. They also suck up a few tiny bugs on their way to get protein. Your flight is a wonder to behold and hear. Their name, of course, comes from the deep hum of their wings, which beat so fast they’re almost invisible.
The special powers of hummingbirds
The approximately 330 species of hummingbirds — all native to the Americas — are the only birds that can fly forward, backward, and soar. They can fly up and down vertically like a helicopter and even perform somersaults and other aerial acrobatics. Men in particular court women with aerial acrobatics that seem impossible even when observed. Additionally, despite their small size and high energy requirements, ruby-throated hummingbirds fly 600 miles uninterrupted twice a year across the Caribbean Sea while migrating to their tropical wintering grounds. If birds generally perform amazing physical feats, the feats of hummingbirds are among the most amazing.
If that were all you knew about these hummingbirds, you would no doubt expect them to be short-lived. After all, they live in the fast lane, and with rare exceptions, animals that live fast die young. But you would be wrong. Ruby-throated hummingbirds can live more than nine years in the wild, although they make their death-defying flights over the Caribbean Sea twice a year. They are also not the longest-lived hummingbird. The similarly sized broad-tailed hummingbird (Selaphorus platycercus), with similar energy requirements, can live for at least 12 years in the wild. The much larger mouse lives only a few months in the wild and only about three years as a well-cared for pet. Therein lies a secret that, once fully understood, can help devise ways people can stay healthier longer.
What is the secret of the birds?
Hummingbirds are an extreme example, but virtually all avian biology can be understood in terms of adaptations to the extraordinary energy demands of powered flight. These energy requirements all suggest that birds should be short-lived, but they are the opposite. Their body temperature is higher than ours; Their resting metabolism is up to twice that of a mammal of the same size, and during flight their metabolism revs up even further. Even gliding flights, performed by gulls, vultures, and albatrosses, seem almost effortless to us, but they double or triple the birds’ resting metabolism. Fuel for their extraordinary energy needs is provided by blood sugar levels, which in humans would signal uncontrolled diabetes. Uncontrolled diabetes resembles accelerated aging more than virtually any other disease.
High energy, high heat, and high blood sugar should speed up a number of the key processes that contribute to aging, one of which is free radical production. Remember that free radicals are molecules that can damage all classes of biological molecules, including DNA. To maintain cellular health, free radicals must be destroyed quickly by our antioxidant defenses, and the damage they inevitably cause must be repaired quickly. Birds must have exceptionally potent antioxidant defenses and exceptionally rapid repair mechanisms. In fact, some of the few studies that have been done to understand the longevity of birds have found that their cells produce fewer free radicals at the same rate of energy production as similarly sized mammals. However, we don’t understand how they do it. They can also withstand more free radical damage before their cells die. We don’t understand how they do it either.
The other aging process that our understanding of bird aging should accelerate is the browning of proteins. Proteins drive the chemical reactions that define life. To power chemical reactions, proteins must be folded in complex and precise ways, like origami. Any slight deviation from the perfect fold will affect their function. Imperfectly folded proteins not only lose their function but also become sticky, causing them to clump together with other misfolded proteins. The plaques and tangles of Alzheimer’s disease are particularly well-known clumps of misfolded proteins, but there are many others.
Proteins spontaneously misfold all the time in the chaotic bumper car environment of our cells and are regularly broken down and their parts recycled. However, a specific type of misfolding protein is slow to recycle proteins and is most relevant to birds and diabetics. This is the browning reaction caused by heat and sugar. Sugars spontaneously attach to proteins and interfere with their precise folding. The higher the heat, the more concentrated the sugar and the faster this browning reaction will take place. It happens very quickly at the temperatures we use when cooking. Because of this reaction, meat and toast turn brown when heated. The same thing happens in our body, just much more slowly. For example, our tendons and ligaments are made of collagen, a protein that tans and stiffens with age. Aging athletes are to blame for the increased risk of injury. Because of birds’ higher body temperatures and elevated blood sugar levels, their tendons, ligaments, and other tissues should tan much faster than mammals. But they don’t.
How birds prevent free radical damage and tanning could benefit human health. Do they have unique antioxidants that prevent free radical damage? Do they have unique ways to break down damaged proteins? They must also have mechanisms that maintain cell function in the face of life’s challenges. There is little research on the aging process in birds, but never a large, sustained effort like we might have if it were being studied for cancer prevention. Medical research remains largely bogged down in studying short-lived laboratory species like fruit flies and mice, from which we may learn little, to improve or prolong human health. A Manhattan project to understand the extraordinarily slow aging of birds and their ability to maintain strength and endurance throughout life would be a good use of research funds.
This article was originally published on The reader from Steven N. Austad. Read the original article here.