Download Wader breeding in Eastern Denmark

Impacts of wet grassland
management and winter severity
on wader breeding numbers in
Eastern Denmark
Niels Martin Schmidt
Wader population development
• Most wader populations are declining in Denmark,
and in Europe in general
100
Index of lapwing breeding in Denmark
90
80
60
50
40
30
20
10
1999
1998
1997
1996
1995
1994
1993
1992
1991
1990
1989
1988
1987
1986
1985
1984
1983
1982
1981
1980
1979
1978
1977
0
1976
Breeding index
70
From Jacobsen (2000)
Wader population conservation
• Large efforts are being invested in reversing this
trend
=> mainly focused on wet grassland management
• Waders also respond strongly to winter severity
• Relative importance of grassland management and
winter severity
The Klydesø reserve
• Area of national interest as wader breeding ground
Lapwing
Redshank
Avocet
Ringed plover
Oystercatcher
• Reclaimed from sea in 1945
=> Situated below sea-level
=> Large succesional changes
=> Detoriation of costal meadow as wader
breeding ground
Population development in the
Klydesø reserve
80
70
Winter flooding
Grazing
Breeding pairs
60
50
40
30
20
10
0
1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001
Lapwing
Redshank
Oystercatcher
Avocet
Ringed Plover
Management implements
• Cattle grazing (app. one steer per ha, 38 - 270 ha)
• Winter flooding (app. 115 ha shallow water)
Expected effects = more breeding and foraging
habitats
• Fox exclusion
Expected effect = less predation on nests
Winter severity
• Proxy of winter severity: NAO winter state
Expected effects of mild winters (high NAO)
• Improved survival when migrating and when on
winter grounds
• Early onset of breeding in years following mild
winters
• Changes in food availability on tidal flats
Population models
• Autoregressive analyses
• Most parsimonoius model selected by AICc
Nt = Nt-1 Nt-2 GRAZING WINTER-FLOODING NAO
Waders, management and climate
Nt-1
Nt-2
NAOt GRt-1
Lapwing
Ringed plover
Oystercatcher
++
--
+
-
0.62
0.82
++
+
R2
0.80
++
Redshank
Avocet
WFt
0.88
0.62
Lapwings and winter severity
Nt-1
Lapwing
(Klydesø)
Lapwing
(Tipperne)
Nt-2
NAOt GRt-1
++
++
WFt
R2
0.80
0.63
Conclusions
• Management implements did result in increased
(most) wader breeding pairs
• Multi-lateral conservation approach needed for
ensure coastal meadow species diversity
• Winter severity may be more important when
management effort is constant
The Lapwing paradox
• Where do the lapwings come from?
80
70
Breeding pairs
60
50
40
30
20
10
0
1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001
• High predation pressure on nests (c. 90%)
=> too low production of young to maintain
population size
The Lapwing paradox
• Underestimation of production of young?
• Attract birds from other (declining) population?
• Production of young in arable areas, e.g. cereals?