Changes in numbers and distribution of wintering Long-tailed Duck Clangula hyemalis in Baltic offshore waters

Forskningsoutput: TidskriftsbidragArtikel i vetenskaplig tidskrift

Abstract

Regular midwinter counts of waterfowl (included in the
International Midwinter Counts, IWC, organized by what
is now Wetlands International) has been undertaken in
Sweden since the start in 1967 and are still going on,
now as a part of the National Environmental Monitoring
Programme. After the first exploratory years including
country-wide surveys in 1971–1973 undertaken both
from the ground, the air and boats, the programme was
standardized to cover an adequate sample of coastal and
inland sites of south Sweden for the production of annual
midwinter population indices for important species
(areas further north in Sweden are normally ice-covered
and without importance for waterbirds in winter). Further
large scale surveys were undertaken in 1987–1989, 1993
and 2004 (country-wide survey). The programme did not
cover the seaducks in offshore areas (later included in a
special programme). The present contribution analyses
the first 40 years of midwinter counts in Sweden, especially
with the aim to elucidate changes in distribution
and numbers of the different species during this time series.
During the period there was a marked change in the
winter weather and especially the ice situation in Sweden
in January, being a factor of importance for the wintering
waterbirds. During the years 1967–1987 there were
five really hard ice-winters, whereas in the latter part of
the period there was no really hard ice-winter. Comparisons
between the country-wide surveys in 1971 and 2004
showed a marked increase from 172,000 to 627,000 individuals
excluding the offshore species Clangula hyemalis
and Melanitta spp. Anas platyrhynchos increased
from 67,000 to 150,000, Aythya fuligula from 54,000 to
230,000 and Bucephala clangula from 19,000 to 75,000.
Increases were also found in most of the other species.
In addition, Anas penelope and Podiceps cristatus established
new wintering traditions in south Sweden. Midwinter
indices for nine out of ten species showed significantly
increasing trends over the 40 years, no species
decreasing. In Anas platyrhynchos and Aythya fuligula
the indices showed fluctuations around a steady level,
then a marked increase followed after the last cold winter,
whereas species like Bucephala clangula and Mergus
serrator showed increasing trends from the start of
the counts. Fulica atra crashed markedly after one cold
winter and remained for years on a low level before recovering
but the overall trend was increasing. To a large
extent the increases found are probably due to the milder
winters in later years, which also led to changes in winter
distribution within the country, also being reflected in the
regional totals for different species. Part of the increases
does also reflect genuine population increases as show by
comparisons with IWC results from other countries.

Detaljer

Författare
Enheter & grupper
Forskningsområden

Ämnesklassifikation (UKÄ) – OBLIGATORISK

  • Ekologi
Originalspråkengelska
Sidor (från-till)135-226
TidskriftOrnis Svecica
Volym26
StatusPublished - 2016
PublikationskategoriForskning
Peer review utfördJa