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Migration

One of the most notable things about just about any bird population is that some of the birds are only present for some of the time or season. Between 1500 and 4000 species of birds migrate, the real answer/s to how and why is not really known yet and the experts differ as to their answers. The following pages in Ecobirds are a brief introduction to extent and mechanics of bird migration (migration also takes place in animals). The examples used are from all across the world, but time, space and information are limited and not all could be included.

Seasonal migration is a major factor in the life of many birds. In some cases this migration is very obvious and involves huge distances but at other times it is much more subtle. In the UK most people know that Swallows (e.g. the Barn Swallow - Hirundo rustica), Swifts and many small passerines such as Wood Warblers and Redstarts are migratory birds. They are present in the summer, but fly south along with many other species to warmer climes for winter. Similarly, many ducks and geese are only present in the UK during winter, when we are their south i.e. they arrive from further north. They return north to the nearctic in summer to breed.

What is less well known is that a number of our more regular birds are migrants as well. Birds that we see all year such as Robins and Starlings either leave or come to Britain during the winter. For some of these species, birds move south a certain degree over their whole range so that though my local birds have left and gone south their more northern cousins have also moved south and arrived. The overall effect can be that to a cursory observation, the population is sedentary when in fact it is quite dynamic. A further complication to this picture is that in some cases only part of the population is migratory. In other words some local birds move south, some remain and some more northern birds arrive. This means that though I see a species of bird, say Chiffchaff (Phylloscopus collybita) all year round, the birds I see come from two different populations. Anyway, whatever the true nature of the migration observed the fact of migration itself is a fascinating and awe inspiring facet of bird ecology.

There is also great speculation about climate change and how this is effecting the movement of birds in local , regional and global scale. For example, a greater number of birders are already reporting an increasing number of rare or new birds in some areas in Europe (this is not only north / south movement but also east / west movement), and others have reported incidences of non-migration that never used to occur in the past. Many birders are monitoring bird movement and/or occurrence more closely, but it will be a while before definite changes in bird movement patterns emerge. In addition, under certain circumstance some birds are known to travel south in some winters but not others. This is not migration, but dispersal resulting from a population boom. These population booms can occur regularly, i.e. every 4 or 10 years perhaps, but there is no return in the spring. Destruction or loss of food resources can also cause the irregular "eruptions" of birds to new habitats.

In Europe, there are certain areas were it is easier to see bird migration than others e.g. there are many locations in Italy were one can see the migrations south in the northern autumn and then north again in the northern spring. There are also certain areas in Scandanavia (e.g southern Sweden) that are excellent what large numbers of birds migrate.

If you have any information you would like to see on this page/site, or suggestions about were and how we get additional useful information, please have a look at the pages on how you can participate in building information and creating knowledge in EcoBirds or please send EcoBirds your comments.

Part of the information on this page was contributed by EarthLife.


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Last updated: 01 January 2003