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Bird Ringing for Science and Conservation
Bird Ringing and Global Climate Change
Birds as highly mobile and easily observable organisms
are extremely responsive to climatic changes. They were among the
first organisms that made it obvious to scientists and the public
that climate is now changing at a remarkable rate. Earlier spring
arrival of migrants, earlier onset of the breeding season, a northward
shift of breeding areas and an increase in winter reports of migratory
species gave clear evidence for a general rise in temperature over
most of Europe.
In several countries bird ringing has been in constant
use for over 100 years and data at national ringing schemes cover
large geographic areas. The recovery database of birds from Britain
and Ireland was used to calculate indices of migratory tendency
which can be used for a variety of analyses, including detection
of changes in migratory behaviour. Based on the same dataset of
ring recoveries in Britain and Ireland, relationships were shown
between mean wintering latitude and climate variables. In a comparable
analysis on the German ring recoveries of 30 species evidence was
found for significantly increased proportions of winter recoveries
within a distance less than 100 km in nine species. Evidence for
reduced mean recovery distances between breeding and wintering areas
was found in five species and a tendency towards wintering at higher
latitudes was found in 10 species.
During the last decades Bee-eaters, a
species of the warmer regions of Europe and Africa, appeared
for breeding in good numbers in Central Europe. Ringing
projects will help to understand if new northern breeding
colonies are self-sustainable or if these colonies need
a steady influx from productive southern parts of the population.
Although heterogeneity of ring recovery data in
terms of ringing activity, recapture, re-sighting effort, recovery
and reporting probabilities of recoveries on a temporal and spatial
scale are problems for these types of long-term
analyses the data from bird ringing offer promising possibilities.
First, ringing and recovery databases cover larger areas and longer
time-spans than most single studies. Second, in contrast to pure
observations and bird counts, individuals with deviant behaviour
(like wintering in northern latitudes by migrants) can be assigned
to distinct populations. Third, the datasets are readily available
in standardised, electronic format. Thanks to the co-ordinating
efforts of EURING, analyses of changes in migration behaviour of
some species might cover many decades and large geographical areas.
Furthermore the success of wintering attempts in northern latitudes,
as well as fitness consequences of changed behaviour in response
to any environmental change can only be measured properly when the
bird is individually marked and can be recognized.
Swifts are among the species with increased
reports of two subsequent broods instead of a single one
per breeding season. But are the parents of both broods
identical or did another pair start a late brood in the
early abandoned nest site of their predecessors? Studies
with individually marked birds can help to find the answer.
Besides the current strong tendency to assign almost
all observed changes in bird behaviour to climate change it must
be kept in mind that also changes in land use, winter feeding, availability
of rubbish dumps and many other environmental changes may affect
the position of wintering areas and the timing of breeding behaviour.
Standardized data from ringing projects and the insights into life
histories of individuals, as shown by ring
recoveries, will help to entangle this complex framework.
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