First published September 1, 2015... Contact Hart at

How do birds keep from bumping into each other when they suddenly ascend, as shown in this mixed flock. (photo 1)

Crowded Skies

Photo 2: Semipalmated Sandpipers

Photo 3: Red Knots

Photo 4: Mixed Flock (Ducks)

Photo 5: Snow Geese

Photo 7: Tree Swallows

Most frequent fliers have heard the dreaded “Our arrival at (insert destination airport) will be delayed due to (insert delay cause: storm, high winds, icy conditions, sleepy air controllers).” At that point the aircraft will join numerous others already stacked up circling the airport, making the skies in the area ever more crowded. Fortunately, the sleepy air controllers in the tower will direct traffic and prevent any collisions. Birds in crowded skies are on their own.

When large numbers of birds take flight at the same time it is amazing that they somehow manage to avoid each other and prevent collisions. Dense concentrations of shorebirds, particularly during migration, often take off in huge numbers when threatened by passing eagles or Peregrine Falcons, or sometimes by thoughtless beach walkers or uncontrolled dogs. The synchronization of their lift off from the beach is breathtaking, and the absence of birds crashing into each other in their haste is truly remarkable. Consider, by comparison, the occasional injuries suffered by human concert goers or European soccer fans, sometimes trampled in the crush of event excitement. (photo 1)

Even when airborne, birds often remain densely packed in close flying flocks, presumably for added protection from predators which may be confused as to which specific bird in the group to target as potential prey. Thus, it is important for each bird in the group to remain in the tightly packed formation, so that it may not be singled out as the Peregrine’s next meal.

It is a sight to behold watching a Peregrine Falcon chase a flock of shorebirds off the beach and out over the surf, trying to determine if one of the sandpipers is not able to keep up, or will stray only slightly away from the tight group, and thus be easier to catch. (photos 2 and 3) Larger birds, such as ducks and geese often rise from the water or their feeding grounds when a Bald Eagle flies over, and without an air traffic controller, they are still able to avoid running into each other, even when they occasionally fly in different directions. (photos 4 and 5) Nevertheless, sometimes the Bald Eagle wins. (photo 6. left) Smaller birds, such as Tree Swallows, also travel in large tightly knit flocks, particularly during migration. (photo 7) See also my previous article on mumumation. Some mixed flocks, such as these Willets and Marbled Godwits are quite picturesque. (photo 8)

Scientists have understood for some time now the advantages of birds, such as geese and cormorants, flying in V formations, as each bird following in the air stream of the bird in front of it gets lift from the draft of the forward bird. But do you know why - when birds fly in V formation, often one leg of the V is longer than the other leg of the V? Answer below. But only recently have studies revealed how birds flying in tightly packed formations are able to move in synchronization without crashing into each other.

Birds need only be aware of the seven closest birds surrounding them: on each wing side, directly in front right, left and center, and in front, just above and below. Birds eyes, located on the sides of their heads, enable them to do this, and their ability to react with split second timing enables them to maintain their position in the flight path. Perhaps the most remarkable demonstration of this ability can be observed in the murmuration of European Starlings as seen in this video: Enjoy the music as well.

And so, my friends, while airplanes in crowded skies need air traffic controllers to keep them from crashing into each other, and humans left on their own at concerts and European soccer matches occasionally trample one another, birds have mastered togetherness without assistance. Engineers are now working on driverless automobiles that are able to navigate crowded highways without crashing. Maybe we are finally getting as smart as the birds. Remember, “birdbrain” is a pejorative. Why is one leg of the V longer than the other? There are more birds in the longer leg.

For an excellent discussion of bird flight dynamics, see: Also: And finally:

Photo 8: Marbled Godwits

Click photos for larger versions