Crowd Control

Watch: Ingenious hawks learned to thwart their prey's greatest defense

They dive into the crowd and leave the rest up to fate.

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Caroline Brighton (Oxford Flight Group)

These bats may think they have the element of confusion on their side.

But their chaotic swarm can’t throw off a hungry Swainson’s hawk.

Caroline Brighton (Oxford Flight Group)

Swarming behavior is a common tactic animals use to thwart predators — or so we think.

It turns out some, like the Swainson’s hawk, know how to foil the defense.

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Writing this week in the journal Nature Communications, researchers pinpoint how the birds successfully snatch a meal from the crowd.

Caroline Brighton (Oxford Flight Group)

For the study, they spent 21 days recording hawk attacks on bat colonies pouring out of the Jornada caves in New Mexico.

Then, they mapped the trajectories of the birds and bats to observe how the predators dive in for the kill.

Brighton, et. al/Nature Communications

Here’s what one bird’s trajectory looked like. The red dot indicates where it caught a bat.

Caroline Brighton (Oxford Flight Group)

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It might seem reasonable that the birds pick individual bats from the crowd and chase them around until they’re close enough to grab the bat with their talons.

But that’s actually not what these predators are doing.

Instead, they focus their eyes on a fixed point in the crowd and dive toward it until they literally collide with prey.

Caroline Brighton (Oxford Flight Group)

“The hawks appear first to turn into the swarm, and then to extend their legs in a grab maneuver directed at whichever bat they find themselves on a collision course with as they close range.”

Brighton et. al, study authors

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Caroline Brighton (Oxford Flight Group)

This tactic works best for the birds in crowded settings, as it raises the chances that they’ll collide with prey while diving toward their imaginary target.

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It also makes the process of snatching prey a lot less confusing for the birds.

The hawks don’t have to track the movement of a single bat as it darts through a giant crowd. They just start diving and leave the rest up to chance.

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The authors hypothesize that hawks aren’t the only ones that use this strategy, and it could be more common among predators than we realize.

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If that’s the case, then strength might not lie in numbers, at least for bats, fish, and other small creatures trying to avoid being someone’s next meal.