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How Do Birds Avoid Crashing When Flying Through Trees?

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We have bird feeders in our backyard and we love to watch the different birds swoop in and out of the yard from the wooded area behind us.  We’ve watched them fly in amongst the branches of the trees and have often been amazed at their ability to avoid flying into the branches, especially as fast as they fly.

We’ve watched the resident Cooper’s hawk chase smaller birds through the trees.  Their aerial acrobatics of turning, tilting, and rising up and down are fascinating to watch.  It kind of reminds us of watching the smaller spacecrafts maneuver in Star Wars.

Or have you ever watched a large flock of birds that seem to turn, twist and move all around in unison without any of them colliding?  In our neck of the woods, we get some large flocks of starlings that easily number over a thousand.  They will swoop, rise, dive, land and take off all at the same time, and I’ve never seen any of them collide.

Professor Mandyam Srinivasan from The Vision Centre, The National Vision Research Institute and The University of Queensland, led a team of researchers to try to determine just how the birds avoid crashes and reported:

As animals travel forward, things that are close seem to speed by, and things that are farther away seem to travel more slowly.  It’s the same for birds. We found that they try to achieve a safe ‘balance’ by ensuring that the background images are passing at the same speed in both eyes.

This means that if the bird flies closer to obstacles on one side, the near eye will see things passing by faster while those seen by its other eye will pass more slowly. This imbalance prompts the bird to veer away to even out the speed of image flow in both eyes.

They started by training budgerigars, also referred to as parakeets, to fly through a corridor with walls lined with horizontal or vertical stripes.  By adjusting the position and direction of the stripes they found that the birds adjusted their speed and their distance from the sides of the corridor.  According to Dr. Partha Bhagavatula, also a member of the team described the results as:

We found that birds fly the fastest when both walls are lined horizontal stripes, because the stripes are parallel to the bird’s flight direction, and the birds don’t ‘see’ a strong image flow in the background.  But when both walls have vertical stripes, birds slow down significantly due to the strong image motion, which shows that birds also regulate their flight speed according to what they see.”

As vertical stripes project a stronger image flow to their corresponding eye, they veer away to restore the balance between the flows experienced by their two eyes.  This was also demonstrated when one wall was left completely blank. Then the birds flew very close to, and occasionally collided with, the blank side.

The researchers said that the information they learned from the study on the birds may help them develop better technology for flying unmanned aircraft, especially through canyons and crowded areas.  Once again, thousands of dollars and hundreds of man hours are being spent to develop the technology that mimics nature and what the same scientists believe developed by pure random chance.

Without this ability to judge the difference in speeds on each side of them, not many birds would have survived living in wooded areas.  They would have evolved living in open places devoid of trees and other obstacles in order to survive.  Not only is flight a miracle in and of itself, but the ability of birds to navigate so quickly on the fly is also a miracle.

When I read studies like this, it reminds me of one of my favorite sections of Scripture, Job 12:7-10 which says:

But ask the beasts, and they will teach you; the birds of the heavens, and they will tell you; or the bushes of the earth, and they will teach you; and the fish of the sea will declare to you.  Who among all these does not know that the hand of the LORD has done this?  In his hand is the life of every living thing and the breath of all mankind.


How Do Birds Avoid Crashes?, Red Orbit, Oct 28, 2011.

Oxpecker and the Giraffe

A delightful nature story in ‘Dr Seuss-style’ rhyme about an oxpecker bird who removes ticks and other nasties from the skin of a giraffe, for the benefit of both.With captivating artwork, it uses these two zany characters to teach about God’s design, and about relationships, in a way that young children can easily understand and enjoy. (Primary/Elementary) 32 pages

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