Let me describe a mystery 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 small, weighing about the same as a US dime. When it is active, it requires so much energy that it must eat up to several times its own body weight in food per day to avoid starvation. During the flight, the wings beat 80 times per second, and each gram of the flight muscles produces up to 10 times the energy of the muscles of an elite athlete 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 fever in humans. It requires so much fuel to maintain this level of energy consumption that, when inactive, it drops its body temperature to the surrounding environment so as not to starve to death while sleeping. The heart hammers away with a machine gun-like 20-something beats per second. Even at rest, it breathes 250 times a minute, about the same rate as a panting dog, to get enough oxygen. Finally, its normal blood sugar concentration would make it dangerously diabetic if it were human.
How long do you think it lives?
I just described a hummingbird – specifically a ruby-necked hummingbird (Archilochus colubris), the species often seen flitting about in 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 some small insects along the way for protein. Their flight is a wonder to see and hear. Their name, of course, comes from the deep hum of their wings which beat so fast they are almost invisible.
The special powers of hummingbirds
The 330 or so hummingbird species – all living in the Americas – are the only birds that can fly forward, backward and hover. They can fly straight up and down like a helicopter and even do somersaults and other aerial acrobatics. Men in particular target women with displays of aerial acrobatics that seem impossible even when you see them. On top of that, ruby-throated hummingbirds, despite their small size and high energy needs, fly 600 miles non-stop across the Caribbean twice each year during migration to their tropical wintering grounds. If birds generally perform astonishing physical feats, the hummingbird’s feats are among the most astonishing.
If that was all you knew about this hummingbird, you’d no doubt expect them to be short-lived. After all, they live life in the fastest fast lanes, and with few 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 across the Caribbean twice a year. They are also not the longest-lived hummingbird. The similar-sized broad-tailed hummingbird (Selasphorus platycercus), with similar energy requirements, can live up to 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-kept pet. Therein lies a secret that, when fully understood, could help develop ways for people to stay healthy longer.
What is the birds’ secret?
Hummingbirds are an extreme example, but virtually all avian biology can be understood in terms of adaptations to the exceptional energy demands of powered flight. Those energy requirements tell everyone 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 in flight the metabolism increases even more. Even gliding, as performed by gulls, vultures and albatrosses, may look almost effortless to us, but it doubles or triples the birds’ resting metabolism. Fuel for their exceptional energy needs is provided by blood sugar levels that would signal uncontrolled diabetes in a human. Uncontrolled diabetes resembles accelerated aging more than virtually any other disease.
High energy, high heat and high blood sugar should accelerate a number of the major processes that contribute to aging, one of which is free radicals. Remember that free radicals are molecules that can damage all classes of biological molecules, including DNA. To maintain cellular health, free radicals must be quickly destroyed by our antioxidant defenses, and the damage they inevitably cause must be quickly repaired. Birds must have exceptionally effective antioxidant defenses and exceptionally fast repair mechanisms. In fact, some of the few studies done to understand bird longevity found that their cells produce fewer free radicals at the same rate of energy production as mammals of similar size. However, we do not understand how they do it. They also tolerate more free radicals before the cells die. Nor do we understand how they do it.
The other aging process that, according to what we understand about aging, should be accelerated in birds is the browning of proteins. Proteins drive the chemical reactions that define life. In their role in driving chemical reactions, proteins must fold in complex and precise ways, like origami. Any slight deviation from perfect folding compromises their function. Imperfectly folded proteins not only lose function, but they 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 in the chaotic car environment of our cells all the time and break down and their parts are regularly recycled. But a special type of protein that misfolds bedevils slowly recycles proteins and is most relevant to birds and diabetics. This is the browning reaction, which is caused by heat and sugar. Sugars will bind spontaneously to proteins, interfering with their precise folding. The higher the heat, the more concentrated the sugar, and the faster this browning reaction occurs. It happens very quickly at the temperatures we use in cooking. Meat and toast brown when heated due to this reaction. The same thing happens in our body, only much more slowly. For example, our tendons and ligaments are made of collagen, a protein that hardens with age due to browning. Aging athletes have been shunned to thank for an increased risk of injury. Because of birds’ higher body temperature and elevated blood sugar concentration, tendons, ligaments and other tissues should brown at a much higher rate than mammals. But they don’t.
How birds prevent free radicals and sun damage is something that human health can benefit from. Do they have unique antioxidants that prevent damage from free radicals? Do they have unique ways of breaking down damaged proteins? They must also have mechanisms that preserve cellular functions in the face of life’s challenges. There has been little research into aging processes for birds, but never a large, sustained effort like we could have done if they were studied for cancer prevention. Medical research remains largely stuck in the study of short-lived laboratory species, such as fruit flies and mice, from which we may learn little to improve or extend human health. A Manhattan project to understand birds’ exceptionally slow aging and their ability to maintain strength and endurance throughout life would be a great use of research dollars.
This article was originally published on The reader of Steven N. Austad. Read the original article here.