Why a V-shape?
If you've ever looked up to the sky having heard a skein of geese overhead you'll be well aware they fly in a noticeable V formation. The same can be said for cranes, ducks, swans and many more migrating species.
V or Y formations are a way for one bird to lead at the point while the rest of the flock spans out behind in two symmetrical lines. It is an interesting pattern but the reason for it is perhaps more ingenious than you realise.
The point bird or leader is doing more than simply leading its flock somewhere new. In fact a flock of migrating birds wouldn't necessarily need a leader as each bird is instinctively able to find its way; they actually all take it in turn to head their group. The reason for the V formation is instead an interesting way for flocks to conserve energy over long distances. It's a technique used by migratory species and studies have shown that a bird flying a long way, as part of a large-ish group, can save upward of 10% of its energy by using this technique. Which could very well mean the difference between life and death.
Each bird positions itself on the wingtip of the bird ahead, and so avoids taking the full brunt of head-on wind. But the brilliance goes beyond even this: the birds have developed a way to match the rhythm of their wing beats to perfectly benefit from one another's updraft! The updraft is formed by an eddy current (one which moves in the opposite direction to the main airflow). So, as a wing beats downward a contrary upward push is formed. Each bird catches the updraft of the bird positioned slightly to the front and side of him, reducing his own effort considerably. Even when flying in pairs, long-distance birds still adopt the same technique, alternating their position as 'wingman'.
Migratory birds can use the sun to know when to begin a journey and use their knowledge of the land to find their way, following rivers and valleys etc. They share the exhausting role of leading a group, following a rotational system that ensures each has his fair share of the hard work. One from the back will make its way up the line to replace the one at the front. Experts are still looking into the reciprocal cooperative behaviour that ensures each bird has his turn, but they presume it was the risks of long migratory journeys that have driven the evolution of such cooperative behaviour in the travelling birds. Research focussing on northern bald ibises [pictured] has been conducted by an international team lead by Oxford University scientists and the University of London.
It seems there's more to a flock of birds than may initially appear and you'll see their innovative V formation crop up elsewhere too: as a basic flight formation for military aircraft, during professional cycling races etc. It's been adopted as a way to conserve fuel and even reduce drag for members of the group. Next time you look up and see a sight like this you're bound to give a second thought to these clever birds and the mechanics behind their careful flight patterns.
Dordogne migration
Impressive flocks of common cranes fly twice a year over Constant during their spring and autumn migrations. Keep your eyes open during late October/early November when the birds are usually crossing the Dordogne on their way to wintering grounds in France and Spain. If you miss them this time round you will have to wait until the end of February/early March when they will be flying back over for their return journey towards nesting grounds in north-east Europe. It's certainly a sight worth seeing. Find out how to stay here for yourself by following the link below.
