Why do birds fly south for the winter?

Black-headed gulls flying in formation.

Black-headed gulls flying in formation. - Credit: Shutterstock

One of my favourite books growing up was Bennett Cerf’s Book of Riddles. A simple book with wonderfully basic yet perfectly descriptive illustrations by Roy McKie.

In addition to a picture, each page had a one-line riddle with the answer revealed as you turned to the next page. Apparently complex questions were answered deftly and often comically with off-beat answers: “Why does a stork stand on one leg?” Quite simply, “Because if he took two legs off the ground, he would fall down.”

It’s the kind of humour I love and which, even to this day, is sure to illicit groans from those who have spent far too long trying to answer the riddle as the complex subject it appears to be. Such was the impact of the simple line-drawings and one-line riddles on my childhood mind that they are now apt to pop-up at any given moment, prompted by everyday events: “What goes up when the rain comes down?” “… an umbrella!”

Over the last few months, I have made regular evening forays to the lakes at Frogmore, just south of St Albans – mainly to walk the dog – and this has prompted a further riddle from Cerf’s book to come to mind: “Why do birds fly south?” It is the question that naturally comes to mind as I watch hundreds of black-headed gulls heading south, often in v-formation and usually accompanied by lesser numbers of other gull species – herring, lesser black-backed and common gulls.

It is a wonderful spectacle and on evenings when the clouds part, the low sun illuminates them like strings of white lights strewn across the sky. They just keep coming, wave after wave, following the line of the River Ver south. For the most part they are silent, unlike their noisy jackdaw neighbours who also stream in, but from the southwest. Even noisier are the ring-necked parakeets that squawk across the scrubland in rapid volleys of tropical green, vanishing into the trees by the lakes.

Ring-necked parakeet

A ring-necked parakeet. - Credit: Steve Round Photography

Both the jackdaws and the parakeets will roost at Frogmore, creating a deafening palaver every evening as they find security in the lake’s island trees. At the very last light the jackdaws will, of one accord, stream up in a great murmuration, perhaps touching one thousand birds. It is a breath-taking phenomenon, often only attributed to starlings, but enacted every night before the birds pour down to roost in the trees, their “chacks” and “caws” finally ceasing.

A jackdaw.

A jackdaw. - Credit: Peter Oakenfull

Standing on the scrubby highland above the lakes can feel like being a traffic policeman in the midst of an avian rush hour, save that I exercise no control whatsoever over the flows of birds. It is for me a liminal moment – a connection with another world and one that I am only able to observe from afar. In this world, birds follow ancient paths, deep instincts and patterns of behaviour that I, for the most part, am not privy to.

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The whole spectacle, sometimes played out above a hunting dog fox or a pair of tentative muntjac deer, brings a sense of mystery but also a welcome certainty to my everyday world. These evening parades are like a timeless clock, ticking regardless of the hour in the human world and set by the sun and the seasons. There is a sense of purposeful urgency in the birds’ movement but no sense of rush – it is the ebb and flow of the daily tide.

Even predators seem unable to break this pre-ordained movement. On two occasions recently I have witnessed a peregrine following the flow of birds – in one instance a two hundred strong flock of newly arrived redwing.

The peregrine approached the flock from behind, adopting an undulating flight – perhaps mimicking a harmless thrush – before darting at one of the migrating redwing. Almost as soon as it attacked the peregrine gave up and sheared off south, away from the unharmed flock. Perhaps the predators find the massed birds a daunting prospect and in this the flock can find security.

The spectacle of flocks on the move is this season’s highlight but the question remains: “Why do birds fly south?” The answer is obvious: “Because it is too far to walk.”