Bird migration: why do birds migrate?
Why do some birds migrate south for the winter and others do not? Where exactly do European migratory birds spend the winter? And when do they return? Discover the answers to these questions and fascinating facts about bird migration in the following article.
For many birdwatchers, the season ends when the birds have finished breeding in the summer and their songs are no longer as vocal and cheerful as they were in the spring. That is, until the cold autumn winds pick up and bring with them a whole new bird spectacle. Suddenly, large groups of birds congregate in fields and trees and huge flocks sweep across the sky. These birds are gearing up for their long and arduous journeys. Because our winters are cold and barren and thus do not offer many bird species the necessary food supply to carry them through until spring, these birds leave their breeding grounds and head south. Keep reading to find out where our native migratory birds go, when they return to us and what dangers they may encounter on their long journey.
Bird migration: What are migratory birds?
Migratory birds are those species of birds that regularly leave their breeding grounds once the breeding season is over to spend the winter elsewhere and then return the following spring. These are often insectivores, such as swallows or warblers, which simply cannot find any food here in winter. However, the European winter offers slim pickings for other bird species as well with simply not enough food to go around. As a result, they are compelled to fly south.
Non-migratory birds are called resident birds, which actually stay in their breeding grounds all year round and make do with what the barren winter landscape has to offer. Our native resident birds in the UK include, for example, the robin, the coal tit and the spotted woodpecker, among others.
How do migratory birds find their way?
Researchers have long been intrigued by how migratory birds navigate their way south. It was discovered early on that migratory behaviour is instinctive in many species and that even animals kept in isolation know exactly where they need to go. Researchers discovered that birds have a kind of internal compass that allows them to perceive the angle of inclination of the earth’s magnetic field. Other navigational tools include landmarks that the birds can learn, as well as the position of the stars and the sun. Birds can determine the latter even in cloudy skies thanks to their ability to perceive UV light.
Migratory routes: Where do our native birds fly to?
Of course, the question now arises: Where do our native migratory birds go when they leave us? Unfortunately, there is no simple answer here. The flight routes and wintering grounds vary from species to species. Some birds migrate only a short distance south, while others travel halfway around the world and still others only migrate under certain conditions. To simplify matters, migratory birds are divided into short to medium distance migrants, long distance migrants, and partial migrants. Read on to find out what these terms mean and which of our native migratory birds fall into each category.
Long-distance migrant birds
As the name suggests, long-distance migrants are birds that cover particularly long distances during migration. Their wintering grounds are usually many thousands of kilometres away from their breeding grounds. The migratory birds fly south from the UK and other parts of Europe over the Mediterranean, along the East African coast and sometimes even across the desert, before finally settling south of the Sahara.
Swifts are a prime example of long distance migrants, spending roughly half the year migrating and only three months each in their breeding and wintering grounds. They are perfectly adapted to life in the air and can even sleep while flying.
Other famous long-distance migrants include:
Short to medium distance migrant birds
Short or medium distance migrants, on the other hand, are bird species that rarely travel more than 2000 kilometres to reach their wintering grounds. Our native migratory birds mainly migrate to the Mediterranean; only a few actually cross the Mediterranean and winter in northern Africa. Some short or medium distance migrants also spend the winter in the milder parts of Western Europe.
Starlings, which can form massive flocks of hundreds of thousands of birds, are among the most well-known medium distance migrants. This makes a truly magnificent natural spectacle!
Other native short and medium distance migrants include:
- Wild geese (such as greylag geese)
- Black redstarts
Partial migrant birds
Bird migration is not always obligatory. Some bird species are classified as partial migrants, which means they are both resident and migratory. Some goldfinches, for example, spend the winter in their breeding grounds, while others spend it in the warmer regions of Western Europe. In the case of the chaffinch, on the other hand, bird migration is mainly a female affair: while the females migrate to milder regions in winter, the males typically stay behind in the breeding areas and form smaller flocks.
Other native partial migrant birds include:
Sometimes bird migration only occurs under certain conditions. In particularly harsh winters and food shortages, some bird species suddenly leave their breeding grounds in large numbers and settle in milder climates. This phenomenon, also known as irruptions or invasions, is seen in birds such as with siskins or jays.
Note: The designations ‘long’, ‘short’ or ‘medium’ distance migrants are always only regionally valid. For example, while the robin is a resident bird in the UK, it is a short-distance migrant in Northern Europe, where it leaves its breeding area and winters in the UK. The same is true for invasive birds that are actually native to more northerly regions and occasionally appear here in flocks as winter visitors. These include, for example, the brambling or the waxwing.
When are migratory birds on the move?
Generally, migratory birds leave their breeding grounds when the breeding season is over and return in spring for the new breeding season. When exactly migratory birds leave depends on the length of their breeding season and the distance to their wintering grounds. Some species leave for the south as early as the end of August; others can be observed here until November. The same applies to their return – while some migratory birds arrive back in their breeding grounds as early as February, others are not back from their wintering grounds until May.
Dangers for migratory birds
Escaping the cold winter is not without its risks. Bird migration is a strenuous endeavour that can be fatal for older birds. But even young and healthy migratory birds have to fight their way through storms and other hardships – one of which is humans and our impact on nature. Due to the intensive use of the landscape such as agriculture and also the increasing sealing of surfaces for roads and the like, resting places and feeding grounds are being lost. In the Mediterranean region, active hunting with nets, sticky traps and other means are also taking place, with many animals losing their lives. Climate change is also affecting migratory birds; due to the increasingly early start of spring, late-arriving bird species are missing the peak season of insects they need to raise their young.
For these reasons, a quarter of all our British native birds are now on the Red List of Conservation Concern.
Despite everything, bird migrations still offer many wonderful opportunities to observe birds. Read our article on birdwatching to find out what you need for this and how you can discover a whole variety of species in your own garden.