Ynglefugle i Vejlerne - Dansk Ornitologisk Forening

220 Ynglefugle i Vejlerne
when a large population used to moult at the site.
The preferred habitats of Shoveler are comparable to
those of Garganey, i.e. vegetation-rich edges of ponds
and gullies. The most important locality is Bygholmengen
where 55% of all mapped pairs, and 36 of 38 nests
have been found in 1978-2003.
There is a major surplus of males, with 74% of all
mapped birds. Incidents of conrmed breeding only represent
less than 6% of the mapped population (Table
19).
There is a positive and signicant correlation between
the population size and precipitation in May, 1978-2003.
And for the part of the birds breeding in Bygholm Vejle,
a positive correlation was found between population
size and water level in March-May. Hence higher water
levels are important already in early spring, and it is important
that the meadows are maintained wet by continued
precipitation later in spring.
Vejlerne is one of the most important breeding localities
in Denmark, and held 3-5% of the national breeding
population of 800-1000 pairs in the mid-1990s. Following
the massive increase in numbers after 1998, Vejlerne
most likely now hold well above 5%.
Pochard was one of the most common breeding ducks
in Vejlerne in the 1920s and 1930s with several hundred
pairs. A count in 1966 witnessed that a major decline had
happened, but the recorded 50-100 pairs (females) still
represented the most important known breeding concentration
in Denmark.
Since 1978 Pochards have been mapped in Vejlerne
from mid April through the end of May, and later in
the season all broods have been recorded (Table 25,
Fig. 35). Only obvious paired birds have been included
as breeders. The breeding population has uctuated
without any trend, and the number of broods even more
(Fig. 35). Some parts of the 25-years monitoring period
show parallel uctuations in the numbers of pairs and
recorded broods, e.g. 1996-2000, but in 2001-03 fewer
broods have been recorded despite a major increase in
the breeding population.
Most Pochards bred on localities that also hold Blackheaded
Gull colonies. Bygholm Vejle north of Krapdiget
held on average 16% of the population in 1978-94; this
proportion has more than doubled following reestablishment
of the dike, associated water level rise and establishment
of Black-headed Gull colonies, with 34% of
pairs recorded in that area 1995-2003.
The Pochards of Vejlerne represent 5-8% of the Danish
population, and Vejlerne holds one of the largest
con centrations of breeding birds in the country. The decline
observed from the 1920s to the 1970s has been
stopped, and after a period with stable numbers an increase
has been obvious in most recent years.
Tufted Duck. Before 1978 most accounts indicate a
breeding population of approx. 50 pairs. Paired birds
have been mapped in May since then, and broods recorded
later in summer since 1979 (Table 26, Fig. 37).
Mapping Tufted Ducks in Vejlerne unfortunately in-
volves a lot of uncertainty, because there is a large nonbreeding
population using the reserve in summer. The
data nevertheless demonstrates a somewhat increasing,
albeit heavily uctuating population, and in 1999-2003
approx. 100 pairs were counted. Even larger uctuations
are seen in the number of broods, and there is no relation
between the estimated population and the number
of broods recorded.
A large share of the population and a larger of nests
have been recorded in conjunction with Black-headed
Gull colonies, and just as for Pochard, an increasing proportion
of the population has been found in Bygholm
Vejle north of Krapdiget.
The population in 1978-2003 was positively correlated
with the temperature in March and with precipitation
in April. Additionally the population in Bygholm
Vejle was positively correlated with the water level in
the same area in March-May. It thus appears that Tufted
Ducks prefer early warm and humid springs and a high
water level in the reed and bulrush swamps.
The population of Tufted Ducks in Vejlerne has represented
8-16% of the total Danish population of 800-1000
pairs, and no sites of comparable importance are found
elsewhere in the country.
Scaup might have bred in Vejlerne in the 1930s, but the
records are poorly documented – and remain the only
potential evidence of any breeding Scaup from the area.
Red-breasted Merganser has throughout most of the
20 th Century been considered a far from common breeder
in Vejlerne, but a more comprehensive study of the
breeding ecology of the species in 1966 revealed 59
nests, and an estimated population of 75-100 pairs.
From 1978 to 1984 it was attempted to count the Redbreasted
Mergansers with the methods as those gene rally
applied to the other ducks, viz. mappings of pairs, but
this counting method was discontinued later, because it
be came obvious that Vejlerne hosted a large number of
non-breeding birds throughout spring and summer. In
later years, the only data compiled was thus conrmed
bree ders, i.e. occasional nest-nds and counts of broods.
Annual numbers vary between zero and 10 broods.
Marsh Harrier probably established a breeding population
in Vejlerne in the early 1900s, and in the 1930s the
population had grown to 20-25 pairs. Later the population
declined, and Vejlerne only hosted between 4 and 10
pairs from the mid-1960s to the mid-1970s. Since 1978
the population has been mapped on an annual basis, and
attempts to count edged youngs have been done most
years as well (Fig. 39). The population has been gradually
increasing and reached 40-50 pairs in 2000-03. Three
quarters of the breeders are found in association with the
largest reedbeds, i.e. at Bygholm Vejle, Selbjerg Vejle
and Tømmerby Fjord.
The development in the local breeding population is
parallel with that of the national population. Following
protection from shooting in the breeding period since
1922, the population grew through the 1930s and 1940s,