Ynglefugle i Vejlerne - Dansk Ornitologisk Forening

transect", has been undertaken every year. This transect
showed a gradual increase to the best year 1996, yet uctuating
en route. After 1996, and especially after 1999,
there has been a very fast decrease, and 2000-03 saw the
lowest numbers ever.
In Vejlerne the Sedge Warbler is distributed along the
edges of all larger reedbeds, often where willow bushes
invade the reeds, and in surrounding agricultural lands
under abandonment.
In spite of the unexplainable almost-disappearance
from the "Selbjerg transect" (which for many years was
seen as a nucleus habitat for the species), many places
exist in Vejlerne and in the surroundings where it is still
common. No intent has been made to do a proper mapping
of all Sedge Warbler territories in the whole of Vejlerne,
but a qualied estimate was made in 2000 by an
observer with a thorough knowledge of local conditions:
1180 pairs (from 646 mapped territories and the rest approximated
according to suitable habitat available). With
a population of this magnitude Vejlerne is Denmark's
most important area for the species. The national population
was calculated at 3900 pairs in the 1990s, after the
species disappeared from large parts of East Denmark.
Vejlerne has a potential to remain a core area in the future,
if management succeeds to preserve sufcient heterogeneity
in the zones bordering reedbeds.
Marsh Warbler was rst mentioned from Vejlerne in
1973. In that year an advance took place north of the
Limfjorden with new records in several places where
the species never had been seen or heard before. Since
1978 all singing males have been mapped each year (Table
43). An increase has taken place during the period
surveyed, in agreement with a general positive national
trend, however somewhat larger variations have been
seen in the Vejlerne material. Marsh Warbler has been
found primarily in agricultural lands surrounding Vejlerne,
especially in overgrown areas where former grazing
has been abandoned.
Reed Warbler. In areas where the reeds grow high and
dense, Reed Warbler is common, and has been so since
the earliest descriptions by ornithologists in the 1920s
and 1930s. It is one of the most abundant species in the
Vejlerne reserve; the population probably numbering
thousands of pairs. As such the species is not subject to
territory mapping, instead it is being monitored by line
transect surveys, which have provided indexes for population
trends (Table 44). The "Selbjerg transect", the only
regularly implemented of these surveys, shows a marked
increase (with uctuations), and the largest number was
counted in 2003. It is assumed that variations in transect
numbers express reactions to local conditions, even
though more specic mechanisms are not known.
During national point counts 1975-2005 the Danish
Reed Warbler population has shown a long-term, signi-
cant decrease of just over one percent a year, in spite
of the breeding range having grown between nationwide
atlas surveys in the 1970s and the 1990s. The "Selbjerg
transect" gures compared to the national index from
Breeding birds in Vejlerne 229
point counts show a significant negative correlation.
One explanation could be that the population is getting
thinner in suboptimal habitat, while it thrives in large
reedbeds.
There is no doubt that Vejlerne constitutes the most
important area for Reed Warbler in Denmark, just as it is
the case for most other birds with reedbed afliation. By
a cautious estimate the Vejlerne proportion of the national
population is maybe 5-10%.
Great Reed Warbler was registered for the rst time
in Vejlerne (and in North Jutland) in 1971 with several
singing males. From then on and until the late 1980s
the species showed a constant occurrence with up to 9
song territories in one year. However, after this period
of stability for more than 15 years, there were no records
or at the most a single bird registered on a single
occasion (and therefore not considered a breeding bird)
in most years 1988-2003 (Table 45, includes years previous
to 1978).
The birds coming to Vejlerne in 1971-87 are supposed
to represent a population with a core of returning birds
year after year, which is remarkable for a southeastern
species on its nortwesternmost outpost. Great Reed Warbler
needs a well-developed, healthy reedbed, hence rich
opportunities ought to be present in Vejlerne from a habitat
point of view, but as a marginal population it is sensitive
to e.g. climatic variations. Also on a national scale
few Great Reed Warblers reach Denmark in these years.
Bearded Tit reached Denmark after reclamation projects
in the Dutch polder during the 1960s resulted in the
establishment of huge reedbeds, which in turn provided
the possibilities for propagation of a large population of
this species. First time the species was found breeding
in this country was in 1967, including some in Vejlerne.
There were records also from 1968-69, but after the cold
winter of 1969-70 no birds were seen in Vejlerne for
some years. Yet a rapid re-immigration happened, and
for 1974 the reports mention 50-100 pairs. Before the
start of the Field Observatory in 1978 some pretty harsh
winters took another toll on the population. During Field
Observatory years no intent has been made to map the
population; we have merely entered all records of occurrences
in the general database. Furthermore, in 1986 and
1988-96 catching of birds for ringing took place in the
reedbed. Here, this material is summed up and presented
in various ways (Table 46).
Hard winters still affect the species extensively, and
the years 1979-85 and 1987 were entirely without records
of Bearded Tits in Vejlerne. But since a new invasion
took place in 1988 the species has been continuously
present, and in few years the population grew
to a large number. The details of the sequence of events
depend on which statement method is chosen: largest annual
sum and largest gure on a "Selbjerg transect" were
in 2000, while the largest maximum count was in 2003.
On the whole there is no doubt that the last years of the
covered period saw a very large population in Vejlerne.
Several times in the course of time it has been at