Second North American Sea Duck Conference - Patuxent Wildlife ...

SECOND NORTH AMERICAN SEA DUCK CONFERENCE
Leif Nilsson
LONG-TERM TRENDS AND CHANGES IN NUMBERS AND DISTRIBUTION
OF WINTERING SEA DUCKS ALONG THE SWEDISH COAST
Department of Animal Ecology, Ecology Building, S-223 62 Lund, Sweden; leif.nilsson@zooekol.l
u.se
Regular counts of wintering waterfowl have been undertaken as a part of the International Waterfowl
Census (IWC) and (later) the national Swedish Environmental Monitoring Programme since 1967.
After the first years, when one important aim was to study distribution patterns etc, and more or less
country-wide surveys were organized, a network of annually surveyed sites was established for the
calculation of annual indices. In addition to these about 25 larger sites, a number of smaller counting
units were also counted. Country-wide surveys (also including aerial counts) were undertaken 1971-
74, 1987-89, 1992-93 (partial) and 2004, covering all ice-free inshore coastal waters. In this poster
I will present the winter distribution patterns and changes in the distribution pattern of sea ducks in
Swedish waters in relation to habitat factors also comparing the occurrence of seaducks in brackish
Baltic waters in contrast to more marine North Sea water on the west coast. I will also analyze
the population development in Swedish sea duck populations during the period 1967-2004. The
commonest species of diving ducks in the Swedish inshore waters in January 2004 were Aythya fuligula
(220,000), Bucephala clangula (73,000) and Somateria mollissima (49,000). For the commonest
species, Clangula hyemalis, only 37,000 were counted in inshore waters, whereas the population
wintering on offshore sea shallows in Swedish water is estimated to be at least 1 million individuals.
During the survey period marked changes were noted for several of the species studied both as trends
in the numbers counted and changes in the distribution. Thus a number of species showed increasing
trends over the study period, e.g. Aythya fuligula, Aythya ferina, Bucephala clangula, Somateria
mollissima,and Mergus serrator. Some of these trends reflect genuine population changes, whereas
other trends are related to changing winter conditions, with a series of milder winters in the latter part
of the study period. Some species showed marked changes in the winter distribution during the period,
thus Aythya fuligula and Bucephala clangula decreased in the south and increased in the northern part
of the coast.
100 ANNAPOLIS, MARYLAND, USA NOV. 7-11, 2005