Candice Bagley
by on December 4, 2020
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Food and nesting space are simple answers! Birds migrate to improve their chances of survival and reproductive success, and while temperature may influence migration, birds can survive in very cold conditions. Their main reason for migrating is to follow their stomachs (aka food) and find safe spaces to nest. It’s one of the wonders of the natural world and, if you’re fortunate enough to witness migrating birds en masse, it’s a spectacular sight.

Many birds migrate in line with vegetation changes. Wind, precipitation, and temperature affect the changes in vegetation and consequently available food and space for nesting - which is why migration is seasonal. These resources and conditions make areas more live-able at various times of the year. Migrating to areas with more abundant resources improves chances of survival and also impacts breeding success.

Such a phenomenon has long-since inspired curiosity amongst scientists and researchers. Until the early 19th century, there were some wild ideas to explain why bird populations were suddenly absent for certain parts of the year.  For example, Aristotle believed that some birds went into hibernation and 17th century English minister, Charles Morton, claimed that birds flew to the moon and back each winter. However, in 1822 real evidence came to light when a hunter in Germany shot down a white stork with an arrow impaled through its neck. The arrow turned out to be from central Africa confirming that the stork had travelled thousands of miles. Following this, in 1906, scientists began to put rings onto the white storks to learn more about where they wintered in sub-Saharan Africa. Since then, incredible advances in technology and satellite tracking have enabled researchers to explore in great detail what happens during bird migration and answer some of the many questions.

 

Where do birds migrate to? 

As food is one of the primary reasons for bird migration, their travel is linked directly to the availability of vegetation. Many bird species therefore leave areas of depleting vegetation and arrive in areas with increasing density of vegetation. Many birds migrate between the Northern and Southern hemispheres. Birds migrate along lines called 'flyways' which offer the best paths for birds. The birds leaving Europe during its autumn usually fly east and west to try and avoid the 'barrier' of the Mediterranean Sea. Smaller birds, with enough energy to keep going will cross wherever they can, however larger birds will often make towards the narrowest crossing points. 

Birds in North America fly towards Central and South America. The paths they choose are usually following coastlines or mountain ranges. Whether they are travelling a few miles or thousands, birds are migrating to avoid conditions that are a threat to their survival. Winter in North America means that the flowers that the ruby-throated hummingbird drinks nectar from disappear, leaving no choice for them other than to travel to Central America for the winter where food is plentiful.

The map below shows the eight major migratory routes that the migratory bird species follow.

Source: Birdlife International

 

These migration routes have developed over thousands of years of adaptation. Due to competition for food and nesting space, it is likely that some species have ventured further from their usual habitats. Climate change and human impact have also taken their toll on bird migration. National Geographic writes that conservationists estimate that every year between 11 million and 36 million birds are captured or killed in the Mediterranean region alone, threatening birds like the chaffinch and the blackcap. Habitats in sub-Saharan Africa have also become less welcoming as increasing agriculture means that more land is cleared of the vegetation vital to some bird’s survival.

 

Which bird migrates the furthest? How far do they go? 

The Arctic Tern, tiny as it might be, is known as the world's longest migrator. Every year, this little bird flies from the Arctic Circle to the Antarctic Circle, an arduous round trip of about 30,000 kilometres (18,641 miles). However, because they follow a strange zig-zagging pattern that means they don't have to fly into severe winds, the journey is probably longer every year. Arctic terns are perfectly built for migration. They prefer gliding in the air, letting ocean breezes carry their lightweight frames for great distances, they can even sleep and eat whilst gliding! 

Source: Go2Moon

 

The Bar-tailed Godwit is another bird with a lengthy migration, travelling from Alaska to New Zealand. Astoundingly, they do not stop along the way, flying more than a quarter of the way around the world (a distance of around 11,000km or 6,835 miles) for 8 or 9 days straight. It’s the longest non-stop migration ever recorded. To complete this incredible feat, the godwits, like many of their long-haul cohorts, have to prepare before undertaking the journey. They spend weeks building up huge fat reserves (essentially their fuel) so that by the time they leave, more than half of their bodyweight is fat.

 Source: JJ Harrison, Bar-tailed Godwit, Tasmania, Australia

 

How many bird species migrate? 

Nearly half of known bird species, around 4000 species, are classified as regular migrants, meaning they make their international journeys every year moving from one habitat to another with the changing seasons. As we learn more about the habits of birds in tropical regions, this number is likely to increase. Not all bird species need to fly to migrate. Many populations of penguins migrate by swimming and Emus, the large Australian bird, will often travel for miles on foot to find food.

Of these 4000 or more species of migrant birds, most breed in the northern latitudes of the hemisphere. To fulfil their migration goals, these species will all follow different patterns be it in route, speed and timings. Some complete their migratory routes in a very short time, particularly certain aquatic species, and others will make a more leisurely trip, often stopping along the way to feed. Some species of warbler are known to take up to 60 days to travel from their winter habitat in Central America to their summer breeding areas in Canada. Many of the smaller species migrate at night and feed by day and others migrate primarily in the daytime.

Huge Flock of Snow Geese Migrating South 

 

How do migrating birds know where to go? 

Many birds are known to follow landmarks, such as rivers and coastlines, although there are many who are comfortable flying directly over large bodies of water on their routes. In 1951, German ornithologist Gustav Kramer performed experiments that showed that European starlings relied on the sun as a compass during their migration journeys. For those species that migrate at night, ornithologist Stephen Emlen conducted planetarium research that showed that the same can be said for the impact of the ‘star compass’ as a navigation tool. Extensive research has also shown that birds possess an internal magnetic compass which they use to orientate themselves along with cues from the sun and stars. There are also some species of bird have a mineral called magnetite in their beaks, which may help their navigational skills as it is sensitive to Earth's magnetic field.

Flock of migrating Canada Geese flying at sunset

 

There are many species, particularly waterfowl and cranes, that follow the same migratory route year after year, even using the same stop-off points because of their plentiful food supply. Some young birds also learn the routes from their parents. If the birds are raised in captivity then humans have been known to teach them, this video shows whooping cranes being taught to migrate by a light aircraft!

 

Where can I go to see migrating birds? 

There are a huge number of places globally that you may catch migrating birds. Many birds stop off for refuelling at key places along their migration routes.

In North America, the birds that migrate do so in the late summer through the autumn (fall) and in the late winter through the spring and generally follow a north-south pathway. As birds fly overland for long periods of time, there are many places to spot migrating birds. Cape May Point in southern New Jersey is a known stop-off point for migrating hawks making their way south. The Finger Lakes region of upstate New York attracts waterfowl in fairly high numbers and more than half a million Canada geese pass through the Montezuma Wetlands Complex, near Seneca Falls. In southern Arizona, a collection of mountains known as Sky Islands fills with hummingbirds on their way north from their breeding grounds in Mexico.

 

Avocet migration over the North Sea

 

France is also a popular location for many species because of its geographical position and diverse ecosystem. However, the birds are not usually there for long, cranes pass over France in just 24 hours so the window of opportunity is small!

Autumn in the UK is a brilliant time to see birds arriving and heading off in their thousands. There are many great locations to view migrating birds from Blakeney Point in Norfolk to Land’s End in Cornwall. The remote Orkney Islands are a well-known birding hotspot in September as all the finches and thrushes pass through and the seabird migration reaches its climax.

 

Where do you live? Have you seen birds migrating near you? Download the Chirp Birding iOS or Android app and start posting your migration sightings.

 

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