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Bird Ringing for Science and Conservation
Bird Ringing as a monitoring technique
In 2001, EU countries committed themselves to halt
biodiversity decline by 2010, and to evaluate this target. Beyond
legal obligation, monitoring – the study of variation in space
and time of bird populations – is a tool for acquiring knowledge
on which good conservation practice may be based. Monitoring is
also the main source of information to alert the general public
on the status of biodiversity and thus contributes to conservation
by affecting policy and behaviour.
The general aim of monitoring is to document changes
in numbers. For most bird species, direct counting is far more cost
effective than ringing to achieve this aim. But counts alone are
inefficient for determining mechanisms and for inferring causes.
From one year to another, change in population size is the result
of a long list of demographic events: reproduction, juvenile survival,
dispersal, recruitment (new individuals entering the population),
adult survival, etc. Most of them can be monitored efficiently through
ringing. Hence, an appropriate monitoring system using ringing may
be able to determine which of productivity or survival drives population
changes, whether population are regulated and thus more prone to
be resilient to global changes, etc. Moreover, long-term time series
allow correlation of demographic rate variation with climatic fluctuation.
Combined with other methods of bird monitoring, monitoring by ringing
allows prediction of the fate of a bird population facing climate
changes.
Ringing data can be used to determine
survival rates of long-lived seabirds such as the Common
Tern.
Monitoring through ringing may either rely on intensive
co-ordinated schemes or be the outcome of the accumulation of long-term
database. The former is best illustrated by the “Constant
Effort Site” scheme (CES; also known as “Monitoring
Avian Productivity and Survival” in North America, an acronym
that speaks for itself). Initiated in 1983 in the UK and Ireland,
CES is currently organised in 16 EU countries, on 600 sites where
over
100,000 birds are caught annually. CES is unique in producing annual
indices of reproductive success of more than 30 species throughout
Europe. CES data have, for example , shown that hot weather in spring
was negatively affecting productivity of already declining species.
This suggests a link between climate warming and
long term population trend through reproductive success for a large
number of species. The production of annual indices of productivity
at a European scale is under study and is likely to be achievable
in the near future. The long term ringing database is also most
useful to monitor changes, through time, of key demographic parameters
of bird population. Among them, changes in migration route, migration
timing and migration probabilities are the most evident. Last but
nor least, one of the few globally threatened bird species for which
Europe has the main
responsibility, the Aquatic Warbler, is almost entirely monitored
through ringing, allowing us to determine the stability of the stopping-over
network from Western Russia and Poland to Spain.
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Great Tits easily accept
to breed in nest-boxes which renders them accessible for ringing.
Hundreds of thousands have been ringed for long-term population
studies that provided fundamental insights into evolutionary
processes, population dynamics, breeding biology and behavioural
ecology. |
The most useful monitoring schemes are those that
cover a large scale and that may be run in the long term. Although
CES is showing the way, there is considerable room for improving
the efficiency of monitoring by ringing. Another direction of improvement
is the continuous integration of different monitoring schemes. This
means more organisation and support for the volunteers who make
up the only network able to monitor biodiversity throughout Europe.
This is achievable by encouraging scientists to work in close association
with ringing schemes.
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