Ynglefugle i Vejlerne - Dansk Ornitologisk Forening

population in Vejlerne a parallel development has been
seen elsewhere throughout Denmark, and factors affecting
this development are probably found outside
Vejlerne and a common feature for the whole Danish
popu la tion. Vejlerne held approx. 10% of that population
around 1990, rather notable for a species that only
estab lished itself in the area 10 years earlier, and far
away from the main Danish breeding concentrations
of Southeast Denmark. The national population around
2000 is judged at 300-500 pairs, and Vejlerne must have
been one of the most important sites for the species in
Den mark, given the high population levels of Vejlerne
in 1999-2003. Although several pairs might attempt to
breed, they appear to have a rather poor breeding success,
because cases of conrmed breeding only represent
4% of the mapped population (Table 19).
Common Teal was a rather common breeder in Vejlerne
itself, and especially in the surroundings of Vejlerne in
the 1930s, but since then the species has almost disappeared.
The species breeds in nutrient poor wetlands,
and the disappearance of the species is probably related
to increased eutrophication of their former breeding habitat
and its resulting overgrowth.
Since 1984 the annual population has been estimated
between zero and seven possible breeding pairs. Evaluation
of the breeding population is however very dif-
cult, because many birds spend the summer and moult
in Vejlerne.
Mallard is a common breeder in Vejlerne, in fact so numerous
that a precise mapping of the population is considered
impossible. The population development is thus
estimated as a relative index, based on the number of
observed pairs plus stationary males in a 15-20 days period
of late April and early May each year since 1978,
and since 1984 all broods have been recorded as well
(Table 21). There is only a weak tendency of parallel developments
in the index and the number of females attending
broods, suggesting large variations in breeding
success (Fig. 30).
Pintail. There is no evidence that Pintail should have
ever been a common breeder in Vejlerne, perhaps except
im mediately after the embankments. The species has
been mapped throughout spring (but primarily May)
since 1978, and all found nests and observed broods
have been recorded (Table 22). The number of pairs consi
dered true breeders has only rarely been over ve, the
rest of the mapped pairs listed are only probable breeders.
In Denmark most Pintails breed along the coast on
brackish meadows and salt marshes, and the total natio
nal population was estimated at 150-175 pairs in the
mid-1990s.
Garganey. Before 1978 attempts to estimate the po pula
tion were very few, with an estimated population of 20
pairs in the early 1970s, but earlier, in the 1930s, the popu
lation was probably considerably larger. Since 1978
pairs and stationary males have been mapped annually in
Breeding birds in Vejlerne 219
May, and the estimated population from these mappings
has been compared to the total numbers recorded every
5-day period in conjunction with the counts of migra to ry
birds from April through June. Additionally all inci dents
of conrmed breeding, i.e. females attending duck lings,
have been recorded (Table 23, Fig. 33). Large interannual
variations in numbers are evident, spanning from
2-4 pairs in the bottom-year 1985 to 85-184 pairs in the
top-year 2000 (when the highest number of broods were
also recorded). The highest number of spring-staging
birds was noted in 1997 with 93 birds.
Garganeys prefer wet and vegetation-rich meadows
with open water bodies. Bygholmengen, the meadows
around Tømmerby Fjord and Vesløs/Arup Vejler have
been the most important breeding areas, together holding
60% of the mapped population.
There is a marked surplus of males in the mappings
with 71% males and 29% females, and it is likely that
all mapped birds do not represent proper breeders. Cases
of conrmed breeding only represent slightly less
than 5% of the mapped population (Table 19). This may
be caused by the fact that Garganeys breed rather late in
the season, hence most broods will be found in the part
of the year when vegetation is high, and eld activities
as well as the chance of seeing the broods are lower than
earlier in spring.
The population size is significantly and positively
correlated with the average temperature in March and
with the precipitation in May, and the number of observed
broods is likewise positively correlated to the May
pre cipitation. Most Garganeys are thus recorded in warm
and early springs, if the water levels at the same time
are kept high by continued precipitation into the proper
bree ding season, this also being evident from positive
cor re lations between the number of Garganeys mapped
at Bygholm Vejle and the water level in the same place
during March-May.
At a national level, Vejlerne is one of the most important
breeding sites for Garganeys, holding perhaps up to
25% of the Danish population.
Shoveler. In the 1920s and 1930s the Shoveler population
in Vejlerne was probably several hundred pairs,
and such high numbers have never bred in the area since
then. A marked decline in numbers was recorded following
the establishment of Centralslusen and the resulting
drainage of the Eastern Vejler after 1965.
Since 1978 pairs and stationary males have been mapped
in May (Table 24, Fig. 34). In addition to the estimated
breeding population, this table also lists all con-
rmed cases of breeding since 1978. The population has
uctuated a lot over the years, with the highest level of
118-303 pairs in the last year 2003, but there is no obvious
trend in the numbers recorded, apart from a notable
increase after 1998. Some relationships exist between
the estimated population size and the number of
con rmed breeding proofs, and with the peak numbers
of Shoveler recorded in autumn after the breeding season
(Fig. 34). In September 1999 636 Shovelers were recorded
in Vejlerne, the highest number since the 1960s,