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Bird migration and climate change

The fact that birds migrate to warmer climates over the winter is something we’re all taught when we’re young, but it’s not that straightforward. Different species migrate at different times, to different places, using different routes – and our actions could be threatening this annual ritual.

Why do birds migrate?

Migration is basically a search for the best food. Our wet summers with lots of daylight hours lead to huge numbers of insects for birds to feast on. However, as it gets colder, more food is available in the warmer climates of Africa and Southern Europe, so many bird species have evolved to include an annual migration between the two climates.

Our long summer days also provide an advantage to breeding birds, giving them more daylight hours to feed their young.

With some birds, such as the Willow Warbler, weighing less than a matchbox, the journey to Africa is full of dangers. However, the advantages of a safer breeding ground with plenty of food far outweighs the risks of a long migration.

While some birds travel south from the UK, in the winter months we host some birds which arrive from further North, where food is in even shorter supply. There are a few species which stay in the UK all year around, but these are in the minority.

What migratory birds come to the UK?

In the summer, we get several visitors who come here to breed, taking advantage of the plentiful food and nesting sites we have to offer. They include:

  • Swallows
  • Swifts
  • Ospreys
  • Gannets
  • Puffins

Over the winter, birds come to the UK from colder climates to the east and north, including:

  • Red wings
  • Lapwings
  • Fieldfares
  • Ducks
  • Geese

How do birds migrate?

Every bird species has its own migration route. Some travel in a straight line to their destination, others will follow landmarks; some stick to flying over land, others cross open water; some take the same route there and back, others will take a different route (known as loop migration).

On some routes, it’s easy to spot the landmarks birds use to guide them, such as following a coastline or river. Some birds use man-made landmarks too, such as roads and railways. Any changes to major landmarks could, therefore, have an impact on migratory routes which may need to be considered. However, birds have a range of other tricks to help them get around, such as their sense of smell and magnetic fields.

The topography of the landscape can also influence the route – many migration routes cross at mountain passes, for example.

Smaller birds tend to have enough energy to keep flying over large stretches of water, so will migrate across seas, whereas larger birds will travel over land until they reach the narrowest stretch of water (such as the Straits of Gibraltar).

Travelling over land also gives larger birds the advantage of catching thermals, which only form over land. This warm air lifts the birds upwards until they are high enough to be pushed across by the wind. Thermals are created by tall features on the landscape, such as mountains, buildings and trees. Creating large buildings or clearing large areas of woodland could impact on the lift birds are able to get, another aspect to consider when planning any development work or change in land use.

What impact is climate change having on migrating birds?

Recent research has shown that migration times are slowly shifting, with birds in North America making their spring migration around 2 days earlier each decade. This doesn’t sound like much, but it does show that millions of birds are being affected in the same way – it’s not particular to one species.

There are concerns that while the migration dates are shifting, other changes such as the emergence of spring plants and insects that birds rely on as their food source, aren’t changing at the same rate. This means that exhausted and starving birds at the end of their migration may not have the food and shelter they need when they land.

This could trigger a knock-on effect where birds miss the optimal time to breed and rear hatchlings, threatening their survival.

Rising sea levels will also have an impact on migrating birds, increasing the distance they must travel. As a result, birds may need to stop more frequently or eat more on these stops to have the levels of energy needed for migration. However, these migration stops will themselves be further apart, and may not even exist – either because of climate change or human land development.

Migration stops are hugely important for birds, as without them, they will not have the energy and strength to continue their migration. Recent plans to upgrade the Gibraltar cable car had to consider the fact that the location is a key migratory stop for some species, so not only have the plans regarded their habitat protection, but also taken into account timings when birds are expected to stop off on the Rock during their migration.

Causing changes to migration routes has an obvious impact on the survival rates of birds during migration, and therefore on bird populations as a whole. As birds are a key part of the biodiversity of many areas, reduced numbers could have a negative impact on entire ecosystems.

What can be done to protect migrating birds?

Climate change is impacting on so many areas now, that anything to reduce carbon levels will make a difference.

For migrating birds particularly, it’s important their habitats are protected all year around – from the places they breed to the places they spend the winter and any migration stops. This requires careful land management, and any development plans should take into account the impact this work may have on migrating species, whether they’re present at that point or not.

To find out about action you can take to protect migratory birds during development work, or how your land can be managed to create a more welcoming environment for bird species, contact us on 01225 459564 or email enquiries@engain.com

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