Ynglefugle i Vejlerne - Dansk Ornitologisk Forening

224 Ynglefugle i Vejlerne
part of Bygholmengen, I have witnessed a major decline
in numbers despite being unable to trace any changes in
management practices and meadow characteristics, at
least with my human eye. The decline after 1990 might
have been caused by a run of very dry springs even at
Bygholmengen, especially in 1991 and 1993.
The Dunlins in Vejlerne are part of the Baltic C.a.
schinzii population. They breed on cultivated meadows
in temperate climates, and used to be very common on
hayfields in the past, but have declined dramatically
in response to changes in agricultural practices on the
meadows. Around 2000 Denmark had 340-360 pairs
of schinzii-Dunlins, and the total Baltic population was
1110-1360 pairs. The meadows of Vejlerne is hence of
major importance to this rare and declining bird, which
today is concentrated into a few good localities with optimal
management. Especially Bygholmengen is of vital
importance to the Dunlins, and it is very important
that management of the meadows helps to secure a habitat
that satises the Dunlin's demands for a nesting site
(short-grazed with water-lled very shallow pools on the
meadows). Conditions to maintain Bygholmengen as a
core breeding site for Baltic Dunlins are present, because
the brackish meadows are unfertilized, and management
can be maintained without major concerns about economical
protability.
Ruff. In the 1930s c. 300 "pairs" of Ruff supposedly
bred at Vejlerne, but judged from sporadic information
from later years, the population has probably declined
continuously at least since the mid-1970s.
Ruffs have only bred regularly at two localities within
Vejlerne, viz. Bygholmengen with 83% of the population
and Vesløs/Arup Vejler with 14%. In the pe riod
1979-2003 the number of mapped chick-alarming females
has varied considerably, from zero in 1996 to 83 in
1988 (Fig. 57). The true breeding population is, however,
probably more constant than the counted numbers
suggest, because variations in numbers of alarming
females is dependent on the birds' breeding success,
i.e. the population will be underestimated in years with
high predation. Fluctuations in the numbers at Vejlerne
from 1979-2003 has to some extent been correlated to
similar uctuations at Tipperne, the most important Danish
breeding site; and it is notable that the four years
with highest numbers were the same at both localities
(1986-89), and that both sites recorded their lowest number
ever in 1996. This suggests that other factors than local
management inuences population size and productivity
of the breeding Ruffs at Vejlerne and Tipperne. It
could be climatic factors, but the parallel decline in 1996
was probably driven by high salinity being introduced to
meadows in both sites the same year, as Ruffs appears to
be sensitive to high salinity in pools on the meadows.
Because the Danish Ruff population has been rapidly
declining, whereas that on Vejlerne has been slowly declining,
the relative importance of the Vejler population
has gone up. In 2000-02 approx. 150 females bred in
Denmark, and Vejlerne held almost 30% of these. If the
species has to survive as a breeding bird in Denmark, it
seems important to secure meadows with heterogeneous
vegetation height, and this is probably best maintained
by combining cattle-grazing with hay-cutting. Additionally
major inputs of saline water from the Limfjord to
the slightly brackish or freshwater ponds and pools on
Bygholm Vejle should be avoided.
Snipe. Prior to 1978 Snipe was considered a common
breeder in Vejlerne, and a single count of the breeding
population recorded more than 100 pairs in 1973. After
1978 rather large year-to-year variations have been obvious
in the numbers recorded (Fig. 58), notably in 1989,
when the population was estimated at 154 pairs, far more
than in the surrounding years. Most years 70-100 territories
were counted. The apparent uctuations might not
represent true variations, because the species is difcult
to count, and the males' territorial display-activities are
highly variable and weather-dependant. Hence the numbers
recorded might at most be considered indicative of
the Vejlernes potential as a breeding site. Adding up maximum
numbers at all sub-localities gives an estimated
total of c. 225 territories. Even that number might be an
underestimate, because some territories have been overlooked.
Four localities together held 87% of the population:
Bygholm Vejle 27%, Selbjerg Vejle 17%, Tømmerby
Fjord 17% and Vesløs/Arup Vejler 26%. A characteristic
feature of the habitats with the highest densities of
drumming males is presence of swampy meadows with
lots of tussocks, and high botanical diversity, most of
which are found in the vicinity of Vejlerne outside the
reserve proper.
Fig. 59 gives the drumming activity of males in the
course of spring. The length of the drumming period
(days from rst to last record) is signicantly and positively
correlated with the population size.
In the mid-1990s the Danish population was estimated
at 2500-3000 pairs, but with considerable uncertainty.
If the magnitude of the population size is correct,
Vejlerne's share probably represents 5-8% of the national
population and is one of the largest concentrations of
breeding Snipes in Denmark.
Black-tailed Godwits started to breed in Vejlerne around
1920 and the population grew to more than 100 pairs in
1964, but declined after that year. 1978-2003 the mapped
population varied between 90 and 219 pairs (Fig. 60),
with a generally increasing trend, and a few major uctuations.
Numbers have grown almost steadily since 1995.
Bygholmengen has been the prime breeding site, with
86% of the population; and the only other regular thus
important breeding site is Vesløs/Arup Vejler with 8% of
the population. One might expect the godwits would benet
from high humidity on the meadows, but I could not
document any correlations between population size and
precipitation nor water levels. The low fox population in
2000-03 probably had a positive inuence on the exceptionally
high numbers breeding these years.
The Danish population of Black-tailed Godwits has
declined since 1980 and at the same time the godwits
abandoned several breeding sites. Presently they are