A new study has looked at movement interchange between two populations of Whooper Swan and its effects on population size estimates. Two different breeding populations of the swan occur in Europe. One is in Iceland, which accounts for virtually all winter birds in Britain and Ireland. The other is in Fennoscandia (plus outliers in the Baltic countries and Poland).
Knowledge of movements, distribution and numbers involved is important in monitoring schemes. Each year a small number of Whoopers stay in Ireland for the summer, and there have been occasional breeding records on lakes in the midlands and north-west.
Using EURING data, the study worked with Whooper Swan ringers across Europe to bring about the total number of birds ringed and to identify out of range movements. More than 18,000 Whoopers have been ringed in 17 European countries since 1979.
Of the 12,324 Whoopers ringed in Iceland, Britain and Ireland, 125 individuals had been seen within the range of the north-west mainland European population, i.e. those that breed in Fennoscandia. Of the 5,958 Whoopers ringed on mainland Europe, only 47 individuals had been seen within the range of the Icelandic population.
The study confirms that interchange between the two populations still occurs (as recently as 2021), although the numbers switching is very low at less than 1%. The research also shows interchange is unlikely to have caused major inaccuracies or biases in the total numbers recorded during the coordinated censuses.
A census carried out across Ireland last year found that Whooper Swans increased by 27%, whilst Bewick Swans look set to be lost from Ireland in coming years. MKO continues to monitor these species during its annual migration, to and from their annual breeding grounds.
Reference: Brides, K, et al. 2023. Interchange of individuals between two Whooper Swan Cygnus cygnus populations, and its effect on population size estimates. Ringing & Migration.
Photo credit: Conor Rowlands, MKO Ornithologist