BSEP116B Biodiversity in the Baltic Sea - Helcom

predation on nests and nesting adults, predation
by white-tailed eagles on nesting adults may affect
the number of breeding pairs in some colonies.
The total number of barnacle geese in the Baltic is
currently estimated at about 25 000 individuals.
Reproductive success, measured as the number of
fledged young per pair, has been shown to be density-dependent
and variable among years (Larsson
& Forslund 1994). The amount of high-quality
grass available around the colonies for newly
hatched chicks in May and June, as well as predation
by gulls, determines the production of fledged
young. Annual survival rates of adults and fledged
young are high. Only limited hunting is permitted
in the Baltic region.
Many, but not all, large colonies of barnacle geese
on Gotland and Öland are situated within protected
areas. The colonies in Finland, Estonia, mainland
Sweden, Denmark, and Germany range in size from
a few pairs to several hundred pairs (Leito 1996,
Mortensen & Hansen 1999, SOF 2006, Koop 1998,
Mikkola-Roos et al. 2008). Some of the latter colonies
have probably been founded by birds of captive
origin. However, birds from such colonies usually
cannot be distinguished from other birds.
Eider (Somateria mollissima)
The main breeding areas of the eider in the
Baltic Sea are Sweden (270 000–360 000
breeding females, bf, in 1999/2000), Finland
(80 000–100 000 bf in 2007), Denmark (25 000
bf 1990–2000), and Estonia (15 000 bf in 1995)
(BirdLife International 2004, Desholm et al. 2002,
Hario & Rintala 2008). The species also occurs in
small numbers in the Russian part of the Gulf of
Finland (70–80 bf) and at the German Baltic coast
(80–100 bf in 2008). The eider does not breed,
or breeds only exceptionally, in Poland, Lithuania,
Latvia, and the Kaliningrad region of Russia.
The eider population showed a strong long-term
increase throughout the 20th century. Simultaneously,
it extended its breeding range southwards
to the German Baltic coast, where the
first breeding was recorded in 1985. However,
since the late 1990s, stagnant or even strongly
declining population trends have been observed
in several countries (Denmark, Sweden, Finland,
Estonia; Desholm et al. 2002, Elts et al. 2008,
Figure 4.3.5). In Finland, the eider is currently
the most rapidly declining seabird species, dropping
down from 150 000–180 000 bf in 2001 to
only 80 000–100 000 bf in 2007 (Hario & Rintala
2008).
This decline is true not only for the Baltic breeding
population, but also for the Baltic/Wadden
Sea flyway population as a whole. Mid-winter
counts suggest that the total population may have
fallen from 1.2 million birds in 1991 to 760 000 in
2000, which is a reduction of 36% (Desholm et al.
2002) 5. Although reductions are evident for several
breeding areas, the decline of the breeding population
along the flyway seems to be less pronounced
compared to the winter population. Shortcomings
in the monitoring of breeding and wintering
numbers, as well as an unknown buffering effect
of non-breeders, are probably the reasons for the
difference (Desholm at al. 2002).
Breeding females
25000
20000
15000
10000
5000
Denmark
Estonia
The recent population development may be influenced
by several factors, among them hunting,
predation by mink and white-tailed eagle, bacterial
and viral infections, parasite infestations, drowning
in fishing gear, and oiling. Low reproductive
success and high mortality of ducklings have been
reported from several breeding areas in the most
recent years. However, several of the factors mentioned
above affected the population already in
74
0
1930 1940 1950 1960 1970 1980 1990 2000 2010
Figure 4.3.5. Development of the eider population in Denmark and
Estonia during the 20th century. Data from Desholm et al. (2002),
Lyngs (2000 and unpublished), and Elts et al. (2008).
5
These population numbers are probably underestimates
because they reflect the counted numbers without any
attempt to correct for birds that have not been seen.
Noer et al. (1995) estimated a population size of 1.5–2.0
million birds in 1990. However, the estimated decrease of
approximately 30%, giving a total population of about
1.0–1.2 million birds in 2000, seems to be realistic (Noer,
pers. comm.).