Ynglefugle i Vejlerne - Dansk Ornitologisk Forening

228 Ynglefugle i Vejlerne
Terns and their faithfulness towards their natal locality
implies that a single or a few years with bad reproductive
results is of less consequence.
It should be highly prioritized in the management of
Vejlerne to extend the area of open wet marsh by grazing
and by mowing, and to improve water quality, because
this habitat is vital for the Black Tern.
White-winged Tern. In 1979 a pair of White-winged
Terns stayed at one of the Black Tern colonies of Vejlerne,
from May 23 till June 11. When the Black Terns
moved from Kogleakssøen to Bygholmengen, the Whitewinged
Tern pair moved with them, and they were seen
warning intensely over the colony. There is no doubt
that the pair attempted breeding, but when the Black
Tern colony was given up, the White-winged Terns too
departed.
Since then White-winged Terns have frequented Black
Tern colonies in Vejlerne on many occasions, but no
further breeding attempts have been observed, not even
during the 1997 invasion, when the species bred at other
Danish localities (and 112 birds were seen in Vejlerne).
The species has a nomadic breeding strategy, and is often
seen in connection with temporarily ooded areas. In
the 1990s it spread westwards from the nearest breeding
sites in Poland, and it is not an impossible thought that
White-winged Terns sooner or later again will join the
Black Terns of Vejlerne at their breeding colonies.
Yellow Wagtail has been breeding on the meadows of
Vejlerne since the 1920s, but only a few concrete estimates
of the population exist before 1978 (for 1973 it was
assessed to be 25 pairs). In the period 1978-2003 there
was a pronounced decrease in population size (Fig. 70),
and at the same time a change, where in the rst years
the majority of pairs were found at the great meadow
Bygholmengen, during the last ten years most territories
were in ditches and along dikes in agricultural lands surrounding
Vejlerne. These areas have been covered less
systematically during breeding birds counts than has the
reserve, for which reason the gures for population sizes
here are less certain.
It seems to be a general trend (also noted in the Danish
part of the Wadden Sea marshlands) that Yellow Wagtail
disappears from marshes and meadows, and breeds in
cereal elds and other crops instead.
Thrush Nightingale reached Northern Jutland at a
late point in its spread westwards in Denmark; and the
spe cies was not annually present in the Vejlerne area
when the Field Observatory begun its activities in 1978.
Singing birds have been mapped during all years since
then (Table 38). In 1994 there were 12, but most years
the numbers have been much lower; the average is
below three. Denitive indications of breeding (apart
from song) have never been noticed. Single birds have
been heard through longer periods, but many were only
registered once or a few times.
Bluethroat (White-spotted subspecies cyanecula). A
female Bluethroat on April 20, 1995, was possibly belonging
to this subspecies, considering the early date.
On April 2, 2002, a male sung in Bygholm Vejle, which
constitutes the rst conrmed record of the subspecies
in North Jutland. These records t in with the immigration
of the species in Southwest Jutland during the rst
part of the 1990s.
Whinchat was found as a relatively common breeding
bird in agricultural lands surrounding Vejlerne before
1978 and also in the 1980s. However, it was not until
1990 a systematic mapping of this population took place.
Since then, at marked decrease has occurred (Table 39),
and this negative population trend in Vejlerne concurs
with a large decrease on a national level (de mon strated
in point counts). Systematic mapping of the Vejlerne
Whin chats since 1990 may be the only documented exam
ple of a specic population being followed by annual
counts in Denmark. Normally, habitat changes are stated
as the reason for this decrease, specically vegetation
suc cession, but in the Vejlerne surroundings this alone
can not satisfactorily explain the decline.
Grasshopper Warbler arrived to Vejlerne only a few
years before the period covered by the Field Observatory.
Since 1978 a few singing individuals have been
mapped in Vejlerne each year but 2002 (Table 40). The
average has been just under four birds. In the last half
of the 20 th Century a large population has built up in
Eastern Denmark, but density is still low in most of West
Jutland.
Savi's Warbler. In the year 1964 this species showed up
at several localities for the rst time in Denmark; thus in
Vejlerne too (three singing birds). Only after the start of
the Field Observatory the species has appeared with regularity
in the area, and every year one or more singing
birds have been mapped, on average just under ve (Table
41). A nest has yet to be found, but several observations
of warning birds or pairs have been made, including
food-carrying individuals. In some cases a specic male
Savi's Warbler has been singing actively for a period of
time, and later it went silent for a long time, but at the
end of the season the bird has had a new brief period of
singing activity.
In addition, six juveniles have been ringed in Vejlerne
during late summer, probably birds hatched here.
The establishment of the species in Denmark seems to
be stagnant, in later years it has become less frequent,
with only 11-23 birds in the whole country in 2000-03.
Sedge Warbler has been a common bird in Vejlerne
in areas free of cattle grazing, since the rst ornithologist's
descriptions of the area in the early 20 th Century.
In 1978-2003 no total mapping has been made of
the breeding population, which has been monitored by
line transect surveys instead. On those transects, singing
birds along specic routes have been counted (Table
42). Only one of those transect surveys, the "Selbjerg