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

SECOND NORTH AMERICAN SEA DUCK CONFERENCE
BREEDING SUCCESS OF COMMON EIDERS
IS AFFECTED BY THE CLIMATE OF PRECEDING WINTER
Aleksi Lehikoinen¹, Mikael Kilpi², and Öst Markus¹
¹Department of Biological and Environmental Sciences, P.O. Box 65, FIN-00014 University of
Helsinki, Finland; aleksi.lehikoinen@helsinki.fi)
²ARONIA Environment, Åbo Akademi University & Sydväst Polytechnic, Raseborgsvägen 9, FIN-
10600 Ekenäs, Finland
Several recent studies have reported that phenology of spring migrating birds is dependent on the
severity of the preceding winter and approaching spring. This severity can be measured using large
scale climatic indices such as the North Atlantic Oscillation index in western Europe (NAO). These
fluctuating indices may also be used as mimics of persistent climatic change, given that they prevail in
one positive or negative mode for several years in a row. Despite the common knowledge that milder
winters in recent years is correlated with persistently earlier migration in many birds in temperate
regions, few studies have been published concerning the effect of climate on variation on spring arrival
and how this relates to breeding success. In northern Europe, the extended winter NAO index correlates
with the ice cover and the timing of the ice break of the Baltic Sea. Ice cover plays an important role
for breeding waterfowl, since they can not arrive to their breeding areas before ice breaks and they
never breed in islands as long as there is an ice bridge to the mainland and between larger islands,
because of increased terrestrial predator risk. We studied the effects of the winter NAO index and ice
break in Gulf of Finland on spring migration, laying date, clutch size, condition of breeding females,
and fledging success of common eider (Somateria mollissima) in 1991-2004 (migration 1979-2004) at
the southern coast of Finland, the Baltic Sea to which eiders migrate from Danish waters during winter.
Body condition of breeding females showed significant positive correlations with NAO, and arrival
dates showed positive correlations and clutch size and fledging success showed negative correlations
with the timing of ice–break. The results suggest that climate, which also affects ice conditions, has
an important effect on the fledging success of eiders. After severe winters females may be in poorer
condition and can not allocate as much to breeding as much as after mild winters. Based on the results,
global climate warming should increase the breeding success of eiders in the study area in the future.
NOV. 7-11, 2005 ANNAPOLIS, MARYLAND, USA
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