| Since the beginning of the
Eighties, the Corncrake population of the Low Angevines Valleys (just to the
north of Angers) has been regularly followed. Counting at night of male
singers make it possible to visualize the evolution of the populations.
Thanks to the agri-environmental measures (OGAFE, OLAE) put in place in the
study zone at the beginning of the Nineties, the population of corncrakes
recovered to reach 400 males singers at the end of the 20th century. In 2000
and 2001, late high waters (May-June, even July in some places) completely
destroyed the reproduction and the population was divided by 4.
Since then we wait for a slow return to "normal" values, to confirm that
this species can re colonise the site if it remains favourable for nesting.
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| In 1995, a first test to
capture the male singers by day is tried: Only one bird is captured.
From 1996 to 2000, only
7 males singers are ringed by this
method.
Fortunately, the English, experts in this matter, publish a new technique
of capture: capture of the males must be carried out at night, from
April to July. The birds are located by their song and are captured using a
scoop with protected edges to avoid wounding the bird.
Thanks to this method, 221 males are
captured in 4 years on the BVA, allowing
several controls of birds previously ringed .
The zone of capture is extended in 2002 to all of France: the objective
is to see possible displacements between the various reproduction sites of
the species. This program, approved by the Research center for the biology
of the populations of birds (CRBPO), is coordinated by Matthieu Vaslin and
Franck Noel.
Currently, the sites involved in this study are as follows:
1. Loire Valley (44), resp. Thierry Roger
2. iles de Loire (44), resp. Hubert Dugué
3. valley of Thouet (49) and meadows of the Minnow (37), resp.
Thierry Printemps
4. BVA (49), resp. Franck Noel
5. valley de la Marne (51), resp. Aymeric Mionnet
6. valley de la Voire (51/10), resp. Stephan Bellenoue
7. estuaire de la Loire (44), resp. ONCFS 44/réserve of Massereau
8. marais poitevin (85), resp. Matthieu Vaslin
The collaborators of the CRBPO wishing to be involved in this study
program are welcome! |
| The following-up of mowing is
an arduous operation, which permanently uses 3 or 4 people from June 20th to
August 10th. Each mowing follow-up is a collection of different data: speed
of the tractor, type of mowing (centrifuges, centripetal, or by bands), the
number of birds observed...
When the mowing is finished, a meticulous visit of the area is carried
out in order to locate the birds which could not have fled.
At the time of the follow-up, the adults in moult
and the young nonflying birds are captured to be ringed. Biometric
measurements (weight, length of the wing, beak and claws...) are carried out
on each bird. They are then released a little distance away in an un-mown
area.
From 1995 to 2003 , 237 young birds
were thus ringed, also 32 adults in moult.
At the end of July 2003, a male in moult is captured during a mowing
follow-up. It had been a ringed male singer 2 months before, 2 kilometres
from there.
In addition, the gizzards of all the dead corncrakes collected at the
time of mowing are the subject of an analysis, in order to compare the
diversity observed in the areas with preferential prey of the crake. In
2001, these analyses gradually extended to other sites, 7 gizzards from
Champagne-Ardenne, 3 from Normandy and 1 coming from Spain were examined.The
whole of the results will be published later..
Realised in 2000 to 2002, this
follow-up makes it possible to visualize displacements of chicks after the
meadows have been mown. The birds are ringed, and then equipped with a
transmitter fixed on the back. Their displacements are followed day by day,
until the loss of the transmitter.
The first results indicate important displacements after the mowing; the
birds follow the networks of ditches to find other not yet mown areas. In
June 2000, a bird equipped with a transmitter after the mowing of an area
was unfortunately run over a few hours later by a mower in the meadow where
it had found refuge...
Unfortunately, for lack of funds necessary for the purchase of
transmitters, this follow-up could not be continued.
During spring and the summer 2000, 13 pots traps
were established on the whole of the BVA, in varied habitats located in
easily flooded zones: meadows for mowing, poplar plantations, border hedges,
mégaphorbiaie. The results are currently the subject of an analysis. The
areas producing the essentials for the corncrake (small invertebrates) are
the lengthily submerged mowing meadows.
Inventories of Orthoptères were carried out and the densities calculated
by the installation of quadrants of a m2: certain areas
accommodate up to 200 000 orthoptères/ha.
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