Fortunately we now know better (or unfortunately if the thought of swallows hibernating at the bottom of ponds entertains you as much as it entertains me). Swallows, in fact, migrate over 10,000 kilometers between their summer breeding grounds in northern Europe to their wintering grounds in southern Africa and back again.
Barn swallows will begin to leave the UK in August with the last having left by September – and young become independent from their parents roughly 1 month after birth. This means that fledgling swallows cannot be learning the migrational routes from their parents. So how do they do it?
The urge to migrate (also called zugunruhe) is triggerd by an internal ‘body clock’ which is synchronised by day length. This ability to track day length is something chicks inherit from their parents along with an instinctive knowlege of the rough direction they must head in. Of course anyone lost in a big city will tell you a ‘rough direction’ wont get you to your chosen restaurant in time for your reservation. These birds need to get to a precise location and their mapping system is pretty extraordinary. Despite their size, these birds tiny brains can use information obtained from the sun, stars, magnetic force fields, polarized light and from land marks to find their way along with their instinctive knowledge of direction and distance. Fortunately for the swallows, It all gets a lot easier second time around – these migratory birds have excellent memories and use land marks to guide their way.
I’ve watched countless documentaries on bird migration, and they are always fascinating – The lastest set of documentaries worth a watch for any bird lover are the BBC Earthflight series. Available on BBC iPlayer for a short while and with clips available after the series is taken down.