Thursday, January 16, 2014

Flapping in Formation

Flocking Habits of Migratory Birds - C. C. Trowbridge 1915 Wikimedia
There has always been a lot of theory and very little fact in the story of why and how some birds fly in formation.  There is probably some benefit to a flock taking off in mass to confuse a predator, a familiar story to a quail hunter flushing a covey.  Maybe the lead birds are better navigators with the latest Google Maps downloaded?  The most popular idea was that they were drafting like bicycle racers and semi-trucks, flying in the slipstream of the one in front to reduce the energy required to fly.

A study by Dr. Stephen Portugal and his team, as reported in the journal Nature provides some better answers.  They planned to use light weight data recorders attached to the backs of birds which flew in formation.  The big technical problem - how to capture the birds to retrieve the data, as transmitters would weigh too much for the birds to carry.  The answer was to use captive-bred ibises.  They used captive-bred northern bald ibis (Geronticus eremita), a species being reintroduced in Europe after being extirpated for 400 years.  They were already trained to follow human foster parents leading  them with ultralight aircraft from breeding areas in Austria and Germany to wintering grounds in the Italian region of Tuscany.  They were easy to tag before flight and to find after landing.

Flight of Northern Bald Ibis - NPR
They found out that not only did they draft but they synchronized their wing flaps to the bird ahead, using the lift of the front birds upwash (the upward flow of air directly ahead of the leading edge of a moving airfoil.)   Not only do they synchronize the flaps but they can adjust to a counter-rhythm when they get closer to find the uplift, as described in this video.

Northern Bald Ibis - Wikimedia
It is heartwarming to know that the starring actor in this adventure was the northern bald ibis (Geronticus eremita), a rather plain bird who would otherwise not get the lead in any bird video.  In spite of a distinguished career of 1.8 million years of thriving across the Middle East, northern Africa, southern and central Europe, it now is nearly extinct, with 500 surviving in Morocco.  A newly found cluster of 10 birds in Syria probably aren't optimally placed for future survival.

In the words of Bill Bryson, "Life just wants to be: but it doesn't want to be much."  Hang in there little buddy.  You may be having a bad hair, or rather feather day but you have an important role in the world, even if it isn't as a leading man or lady.  You are leading us into an understanding of bird flight.

For more details go to the Nature article, then the NPR All Things Considered story.

1 comment:

  1. What a delightful article, especially the bit about "a distinguished career of 1.8 million years of thriving..." I didn't know anything about the northern bald ibis until I heard the NPR piece yesterday. Fascinating study!