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Bird Ringing for Science and Conservation
Understanding Bird Migration - The Need
for Bird Migration
A flying bird can quickly move long distances and
this makes it possible to migrate regularly between areas that are
suitable during different periods of the year. In areas with strong
seasonality, migratory birds can successfully take advantage of
a short but very productive summer to breed and raise young. At
northern latitudes, such as northern Europe, most of the breeding
bird species are migratory and leave for some period of the year.
In most areas of the world, climate and/or food availability varies
over a year. This means that annual movements, in order to increase
survival, can be advantageous everywhere. Migration is a most important
key to the large and fascinating diversity of birds in the world.
The variation in migratory behaviour is extremely
large; some birds move only short distances, while others can migrate
vast distances to wintering areas in the southern hemisphere. Some
species move on broad fronts while others follow very narrow routes.
Irruptive movements occur in several northern species in response
to food shortage.
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Recoveries of Ospreys ringed in
Sweden and reported during the period August-November
show that this species migrates on a broad front.
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The original purpose of bird ringing was to unravel
the mysteries of bird migration. Within Europe the broad patterns
of migration are now known for most bird species. In recent decades
the member countries of EURING have greatly intensified their efforts
in the area of migration research. The computerisation of the archives
of recovery data has been a prerequisite for many of the recent
recovery analyses and also for producing national
recovery atlases. Comprehensive atlases have been published in several
member countries and work has begun on them in a number of others.
This is an important step because it will make results from ringing
easily accessible. It will also show where knowledge is missing
and where efforts in the future ringing should be focused. As migration
pattern change over time, particularly in relation to factors such
as climate change, continued bird ringing is important even for
common species.
Parallel and narrow migration routes
shown by different populations of Chaffinches ringed during
passage at two bird observatories in Europe. Black dots
refer to recovery places of birds ringed at Courish Spit,
Russia (filled square) and open dots refer to birds ringed
at Col de Bretolet, Switzerland (open square).
Migration is a challenge within nature conservation
work since many populations of birds regularly move over huge areas,
and problems en route or in the wintering quarters can result in
declining breeding populations in areas far away. Many migratory
birds are declining in numbers and detailed information about the
annual
movements, including important stop-over sites and winter quarters,
is a top conservation priority.
Large numbers of ringing recoveries are now held
in the EURING Data Bank and they can be used to analyse more complex
questions about bird migration. Results of such analyses could form
the basis of detailed
laboratory and field research into the navigational cues and fuelling
strategies that birds use when migrating.
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