Many of us say we wish we could fly because it looks so fun and calming to travel around in the air. We mean that we would like to be able to glide and soar like a bird. That is why we hang-gliding and use wingsuits that don’t require physical effort. Flying, on the other hand, looks like hard work. They would soon feel pretty sore if you were to flap your arms like a bird for a short period. So why don’t birds get tired when they fly?
Birds don’t get tired due as they manage their energy expenditure. They do this by reducing air resistance and lowering the number of wing beats. Birds also have hollow bones that allow them to fly further, and some can sleep while flying.
If you want to know more, then please read on.
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Why don’t birds get tired when they fly?
If birds became tired all the time when they flew, they wouldn’t survive. They would never have enough energy to travel between destinations, catch their prey, or outpace predators. They must pass without any fatigue risk, just like we would get up and walk whenever required. Still, a long walk can take it out of us, and plenty of birds migrate for long distances.
There are a few different reasons birds have evolved not to get tired when flying. The reasons, and the abilities of the bird, vary between species. Often, it comes down to how often birds use the muscles in their wings and how well they take advantage of their environment. The impact of air resistance is just as crucial as the exertion of energy by the bird. Physical adaptations like hollow bones and more enormous wingspans help too.
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The fewer wingbeats, the better.
Birds are economical with their wingbeats. They don’t use their wings until they have to. That is why you see such large wingspans on a lot of birds. It is much easier for birds like eagles to soar with those large wings and cover long distances without using the muscles to move them.
Eagles and other prey birds will also use thermals and up-drafts to carry them into the air to gain a better vantage point for spotting their prey. They can then circle and swoop across the hunting ground, barely beating the wings before going in for a kill.
The Albatross is an excellent example of a bird with a massive wingspan that doesn’t need to use its wings that much. There are many species, but the biggest is the Wandering Albatross, which can have a wingspan of 11 feet. This bird can travel as much as 10,000 miles in one journey, with some making it in 46 days.
This sounds incredibly tiring, but the Albatross’s wings allow it to do so without expending much energy. That wingspan helps, but they also use an undulating motion in the sky to rise and fall.
The propulsive force of this momentum allows them to travel further without needing to flap their wings. Some go hours without flapping them even once.
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Air resistance
Other seabirds will take advantage of the water to reduce drag and decrease the effort needed to fly. This is why birds like cormorants fly so close to the water whenever they can. This process is called skimming.
There is an interesting phenomenon called the ground effect, where the airflow around a wing changes when it is close to a large surface. This pattern significantly reduces the drag on the wing, which means that the bird doesn’t have to use as much energy to fly. Therefore, it makes sense for birds to get as close to the water as possible and take advantage of this.
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A shorter distance from the water also means less energy getting into the air, making sense for heavier seabirds. There is even a bird called the Skimmer that takes this strategy further. Its bottom mandible is larger than the upper, and it skims the water’s surface for food.
Other birds have alternative strategies for decreasing air resistance and making flying more accessible. For example, Geese fly in skeins with a distinctive V formation. Birds adopt a position a just the right point behind the goose in front to feel the benefit as they pass.
This benefits the whole flock by ensuring they can quickly reach their destination. They aren’t fighting each other to reach the goal; they want the entire family group to make it with as little energy loss as possible. You may have also seen competitive cyclists doing something similar.
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Hollow bones
It isn’t just a lack of wing beats that stops these birds from getting tired in the air. Other physiological advantages help too. Birds are very light creatures. If you have ever held a songbird in your hand to feed them, you know that they barely feel like they weigh anything. It is surprising how this relates to much bigger birds too. Flightless birds are the heaviest species.
One reason for this decrease in weight is their hollow bones. Bird bones are open and light as a simple way to lower the bird’s body weight. They can carry fat for energy during long journeys and offset this with reduced weight in their bones. The less weight there is to move around, the easier it is for birds to stay airborne. They don’t have to flap so hard to get off the ground or to maintain their height in the air. Less strain means less energy expenditure.
In addition, hollow bones are much more robust than you would imagine because of the combination of thin, crossed pieces of bone. This adds strength and rigidity to the skeleton, which in turn helps when using the flight muscles. The easier it is for the birds to create a strong forward momentum, the less tired they become.
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Energy levels
With all of this talk of massive wings and minimal wing beats, we have to take a moment to consider the hummingbird. This bird is the complete opposite. It constantly beats its wings as it travels from plant to plant and needs a lot of energy to stop it from getting too tired. It takes 70 wingbeats a second to stay airborne, and a daily food intake equals three times their body weight.
That rapid flight is so fast that it takes special photographic equipment to slow it down on film and see the individual beat. It all seems counterproductive to us, but many successful species are constantly flying and feeding.
Other birds will eat on the wing to provide enough energy to keep going during long flights and migrations. Swallows will do so and eat as they fly. This gives them the power to overcome fatigue and means they don’t have to stop.
The quicker they get to their destination, the better. Or, they will fatten up before their journey with as much energy-rich food as possible to have enough fat reserve to keep them going. Birds can gorge in Europe at the end of summer and become much skinnier when they reach Africa.
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Sleeping on the wing also helps.
Then some even can sleep on the wing. This is the best way to handle fatigue on a long journey. Different processes depend on the bird, but they are all extraordinary as they allow the birds to fly and rest simultaneously.
One example is the Frigate Bird. This creature travels long distances over water and can’t afford to sleep for long periods. So, it sleeps in short bursts to get rest. Researchers believe that they do so in 10-second bursts – like micro-naps – that add up to 45 minutes of sleep per day.
The strategy of the Common Swift is even more incredible. Slow-wave sleep can occur in one brain hemisphere at a time. Therefore, half of the swift’s brain can sleep while the other stays awake for navigation and survival. There is the potential for both hemispheres to enter this state for short periods when safe, but it isn’t the best approach.
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Summary
As you can see, birds are so well adapted to flight that the process isn’t as tiring for them as you would expect. The strength and lightweight of their bones make forward propulsion easier. More enormous wings and fewer wingbeats lower the risk of fatigue further.
All those birds know how to take advantage of energy sources and their environment to manage energy expenditure. Of course, the Swift and the Albatross have this all figured out best. If you can sleep and fly simultaneously, there is little to worry about.
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Bryan Harding is a member of the American Society of Mammalogists and a member of the American Birding Association. Bryan is especially fond of mammals and has studied and worked with them around the world. Bryan serves as owner, writer, and publisher of North American Nature.