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 the birds that winter in Britain and Ireland. The other is in Fennoscandia (plus outliers in the Baltic countries and Poland). When two populations of the same species may occur in the same place – in this instance wintering grounds – knowledge of movements, distribution and numbers involved is important in monitoring schemes.
The study found limited interchange between the two European populations of Whooper Swan (Glyn Sellors).
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.
Above: Re-sightings of the two populations of Whooper Swan.
The study confirms that interchange between the two populations still occurs (as recently as 2021), although 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
The work also updates the previous estimate of 600 Icelandic Whoopers wintering on mainland Europe to 434.
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. DOI: https://doi.org/10.1080/03078698.2022.2161004
