Friday, October 12, 2007

Bird Flock Movements

Thursday night after the exam, I was sitting on the concrete steps behind Thompson waiting for my ride to come. I looked towards the intramural fields and saw flock of small birds. They were dashing and darting as a cohesive unit. The movements seemed random, but the birds would stay in a tight grouping. This immediately brought questions to my mind.

Zoologist, Wayne K. Potts, conducted an observational study on this manner in 1983. Flocks of Dunlin, a species of bird native to Puget Sound, was filmed using high speed cameras. The maneuvers of the birds were both spontaneous and induced by arrows launched near the flocks. By studying each frame, Potts was able to discern that there was no specific leader of the movements.

The maneuvers could be started by any birds in the group. One bird turning causes its neighbors to turn with it. This chain continues throughout the entire flock until all the birds turn together. He then fired the arrows toward the birds. From these observations he could see that the birds on the exterior, who reacted first, were delayed by their reaction time. However birds reacting to their neighbors could react up to three times faster. This was called "chorus-line hypothesis".

The reason for this behavior is to deter predators. Falcons and other birds of prey are unlikely to fly into a swarm of birds since they could be injured by a collision. This is also the reason behind the movement origins. Exterior birds fly inward toward the rest of the flock, this allows them to be protected while turning away from the risk. If a bird tried to fly away from the flock, they would be very vulnerable.

Well it said that the reaction time of a bird reacting to its neighbor was a 70th of a second and that this was three times faster than a birds normal reaction time. I imagine both these numbers were taken from the frame by frame video analysis that he did. The article didnt say whether the birds kept their positioning or not. I would imagine the birds would pick a spot randomly with the formation of the flock.
Posted by Henry Rafferty (3)


At 2:38 PM, Blogger PWH said...

Huh. That's kind of interesting - instead of doing all the work of avoiding stuff yourself, you can lean on the rest of the flock to figure out just where to go. Out of curiosity, did Dr. Potts have any hard data for the reaction times, or was it just a qualitative sort of test?

Posted by Brad Garvey

At 4:11 PM, Blogger PWH said...

I have always wondered how flocks are able to do this and why. Your blog was quite informative. I wonder if the birds that are on the exterior are always on the exterior or is their position completely random.

Posted by Kathryn DeLisle (3)


Post a Comment

<< Home