Mad About Science: Flocking birds

By Brenden Bobby
Reader Columnist

You will often see gaggles of Canada geese flying overhead during autumn, as they migrate from one place to another. These are the most present and noticeable flocking birds we have in our area.

You may have noticed that geese fly in formation like fighter jets. Ever wondered why? 

Understanding why birds do what they do requires some internal visualization. It’s all about the dynamics of air, and how it behaves when something pushes it out of the way. This is difficult for us to do because we can’t see air, which is one of the reasons we also struggle to keep a lid on irreversibly altering our climate. Out of sight, out of mind.

Courtesy photo.

Even though we can’t see it, it’s important to know that air is there. Every time you walk to work you’re pushing through a three-dimensional wall of air and this generates friction. Not very much, but you would find it a lot easier to move on the surface of the moon. This resistance is called drag, and it’s the reason that we design cars, planes and anything else we want to move fast in a slim, rounded shape. Large, wide objects need more energy to push air out of the way, while something like an arrow pushes through less air to travel.

The presence of air isn’t all bad, however. Planes and birds use air to generate lift so they can climb high in the sky.

What do you think air would look like after something passed through it?

Air likes to equalize pressure wherever it is — similar to water, it’s always looking for “neutral.” When a truck blows past you on your mid-morning walk and you feel that rush of air, that’s air being pushed out of the way by the truck, like snow from a snowplow. If you were to stand directly behind the truck, you would feel air swooshing back into where the truck had been a moment before. Air likes to swirl, a lot like the drain of your bathtub. This swirling motion is important for birds flying in formation.

This swirling motion creates two effects: an upwash and a downwash. The lead bird will flap its wings, displacing air and generating lift for itself. This motion pushes the air directly behind them in a downward motion (downwash), while causing the air behind their wings to swirl upward (upwash). This action generates free lift for birds that are behind another bird’s wings — if they were directly behind the leader’s butt, the air would be pushing them downward and they would have to flap harder and use more energy to stay aloft.

The birds that benefit the most from the formation are the birds in the center of the arms, while the lead bird and the trailing birds are working the hardest to keep flying. Because of this, you will often see members of the formation near the front and the rear swapping places in the formation. It may appear to be a struggle for dominance in a primitive social group, but it’s actually very intelligent teamwork.

You might wonder how birds managed to figure all of this out. As advanced as we are, we can’t “feel” the air when we’re flying. We need a machine to do all of the work for us. We can’t really feel the effort the machine is putting in to fly, therefore we’re just approximating based on what the gauges tell us. Birds know when it’s time to move to a new space in the formation based on how tired they are. As the lead bird or a trailing bird starts to get tired, they’ll begin to slow down — as their neighboring birds have enjoyed the luxury of an easier flight, they’ll begin to overtake the birds that are struggling and relieve them for a break. It’s as simple as that. This is extremely important for migratory birds like Canada geese, which can fly for thousands of miles in a given season.

There is another type of bird flock that functions in a much different way, and produces some incredible results. Starlings are small birds that gather in huge numbers, with flocks of up to thousands of birds. The flocks will blacken out huge sections of sky with what appears to be a gargantuan coordinated cloud that twists, moves and undulates as though they were all of a single mind.

In this form, the flock is called a murmuration, and though it may appear as though the birds (and in some cases, bees and other insect swarms) are communicating through telekinesis or form some kind of hive-mind, it’s actually a very simple trick. One bird marks seven other birds in its visual field. These other birds act as vertices in a grid. Whenever a vector in the grid moves, it deforms the shape of the grid and the starling reacts to the shape of the grid. This causes a chain reaction as that starling goes on to influence the reaction of other birds using it as a reference point.

This may be difficult to imagine as a human. How can the birds react so quickly? This is another case of humans applying our own experience to animals and misjudging the brilliance of nature. Many birds are capable of processing their visual field more rapidly than humans can. Because of this, they experience time passing at a different speed than we do and can track details in a moving mass more effectively than humans.

This is a tricky one to visualize unless you’re of avian descent, but if that were the case you probably wouldn’t be reading this paper.

Stay curious, 7B.

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