The marvel of bird migration

Blog post by Robert Morgan on 17 Oct, 2023

As any birdwatcher will tell you, spring, and particularly autumn, are the seasons of avian migration, and the North Norfolk coast has long been established by ‘birders’ as the place to see this incredible spectacle. Norfolk Wildlife Trust’s Cley Marshes and Holme Dunes coastal nature reserves provide a variety of habitats, and as such, form an important re-fuelling stop for many species. Hundreds of thousands of waders, wildfowl and warblers pass through Norfolk on autumn passage, travelling from as far as the Arctic Circle to the Mediterranean, with many heading deep into southern Africa. Of course, birds such as wild geese, swans and ‘winter’ thrushes arrive and stay with us through the winter. Our swallows and swifts, and many other summer visitors, leave to make the increasingly perilous journey south, only to return to the exact same nest the following year. An enigma of nature that humanity has pondered and marvelled at since ancient times. 
 

In this maelstrom of movement many birds get thrown off course by weather, or simply get mixed into a flock that migrate in a different direction. October is the month that birdwatchers start to twitch, standing-by for news of another rare or unusual bird arriving on our shores from America or Russia. Sadly, most of the smaller birds that are displaced eventually perish. The larger birds often find their way home, but can hang around for months, even years, becoming quite an attraction. A tiny Siberian bird, the yellow-browed warbler, normally heads south into the jungles of Eastern Asia for the winter. For unknown reasons, tens of thousands head west, and several hundred are recorded in the UK each autumn, although being small and unobtrusive, this is probably a fraction of the true number. They quickly disappear, following their relentless, but sadly doomed journey west. A few records report of birds alighting on ships in mid-Atlantic, the fate for most it seems, is exhaustion and death in the vastness of a lonely ocean.         
             

Arctic Tern - Gillian Day

Arctic Tern - Gillian Day

About forty percent of bird species migrate, although local migration does occur among the birds we may consider resident. It’s more often the case that the blackbird or robin that nested in your garden during the summer is not the same individual at the bird table in the winter. A colour ringed blackbird, for five years, spent the summer in Norfolk and the winter in Devon. Migration among most species is generally motivated by an increase or decrease in resources, with movement often prompted by a sudden glut in a particular food. In relation to regions such as the Arctic, isolation in which to nest and raise chicks is the draw. The triggers that sets birds off on their journey, often simultaneously, are probably genetically programmed into the bird, or simply influenced by day-length or position of the stars. Birds will use all or one of several methods to navigate, large birds often take that year’s offspring back with them to their wintering grounds, following long-established migration routes. Others, either as flocks or individuals, use the Earth’s magnetic field, the sun and moon, or the stars to navigate.  
 

It’s hard to comprehend the vast distances that such small creatures cover. New technology, such as miniature geo-locators tracked by satellite, are giving us new insight into their incredible voyages. A seven-year-old female Arctic tern was tagged in the UK at Farne Isle, and during her yearly migration to Antarctica she clocked 59,650 miles. Her rather convoluted route did make best use of global wind patterns, however, it was equivalent to flying twice around the world, with an extra 10,000 miles added for good measure. The longest single journey, was by a bar-tailed godwit, a medium-sized wading bird, which flew for nine straight days 7,145 miles across the Pacific Ocean from Alaska to New Zealand.  
 

It’s not just the astonishing distances, some species of geese will climb to incredible heights, clearing the Himalayas with ease. However, migration, despite the advantages of avoiding the extremes of winter, can be fraught with danger, both natural and man-made. There has been a steady and continuing decline among migratory British birds, particularly those that head to Africa for winter. The reasons for this are very clear, but the list worryingly long:  loss of habitat for summer nesting; decline in insect numbers; draining of wetlands; frequent droughts in the sub-Sahara; excessive hunting; increase in mist-netting and tree liming in North Africa and Southern Europe (illegal in EU countries, but carries on unabated along the Mediterranean coast). This is not just a problem for birds, it is a trend being replicated across the natural world. The European eel population has crashed by 95%, and is just one of many stories concerning the disruption and decline of migratory animals. The Earth, in a healthy state, is a swirling heaving mass of life, in constant flux across its surface, in the air and below the seas. We tamper and damage it at our own great peril.  


Header image - an Arctic tern by Peter Cairns/2020VISION

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