Erratum: Distribution and numbers of moulting non-breeding Whooper Swans Cygnus cygnus in the Baltic States and South Sweden

Abstract

Introduction Feathers wear out through constant use so birds have to replace them. Most birds replace their primary and secondary wing feathers one or two at a time so that their power of flight is not drastically impaired. Swans, geese and ducks, however, shed their wing feathers all at once and consequently lose the power of flight for a period. The Whooper Swan Cygnus cygnus moults its wing feathers from late June to the middle of September and is flightless for about 5–6 weeks (Demenťev 1935, Boiko & Kampe-Persson 2012, Julius Morkūnas unpubl.). Among wildfowl, breeding birds usually moult their wing feathers on their breeding grounds and non-breeders in summer congregations. The Whooper Swan matures slowly and first breeding is usually at the age of 4–6 years (Einarsson 1996). A high proportion of the population therefore consists of non-breeding birds. About two thirds of the population does not attempt to breed in each year (Garðarsson & Skarphéðinsson 1984, Haapanen 1991, Rees et al. 1991, Einarsson 1996, Schadilov et al. 2002, Brazil 2003). Non-breeders of most swan species gather in flocks and undergo wing moult near the breeding Distribution and numbers of moulting non-breeding Whooper Swans Cygnus cygnus in the Baltic States and South Sweden Geografisk fördelning och antal av ruggande icke häckande sångsvanar Cygnus cygnus i Baltikum och Sydsverige HAKON KAMPE-PERSSON, DMITRIJS BOIKO & JULIUS MORKŪNAS Non-breeding Whooper Swans Cygnus cygnus were recorded moulting for the first time in Latvia in 1989, in Estonia in 1993 and in Lithuania in 1997. Moulting has been recorded at 13 sites, three in Estonia and five each in Latvia and Lithuania, but not at all in South Sweden. The total number of moulting non-breeders increased from at least 83 birds in 2003 to at least 187 birds in 2012. The majority of the marked birds found moulting as non-breeders in the Baltic States usually originated from moulting sites within 25 km, the others from countries, including Germany and Poland, situated to the south of the moulting site. Distances between sites of hatching or breeding and moulting for these two groups ranged 0–81 km and 191–836 km, respectively. When caught for ringing, 40% were 2nd calendar year birds, the others older. Life-histories of Whooper Swans marked as moulters, or found moulting, in the Baltic States were used to discuss the lack of known moulting sites in South Sweden. Hakon Kampe-Persson, Pulmaņi, Glūdas pagasts, Jelgavas novads, LV-3040, Latvia. Email: kampepersson@ hotmail.com Dmitrijs Boiko, Natural History Museum of Latvia, Kr. Barona iela 4, Rīga, LV-1050, Latvia. Email: dmitrijs. boiko@gmail.com Julius Morkūnas, Institute of Ecology, Nature Research Centre, Akademijos street 2, Vilnius, LT-08412, Lithuania. Email: juliusmorkunas@gmail.com Received 26 October 2012, Accepted 20 November 2012, Editor: S. Svensson grounds (Brazil 2003). However, Whooper Swans in the Baltic region do not fit this general pattern. No mass-moulting sites have been located in Fennoscandia; only groups of local birds numbering up to 18 individuals in large mire complexes have been recorded (Haapanen 1991, Leif Nilsson in litt.). These groups cannot account for all non-breeding birds, as the number of breeding pairs in Sweden and Finland numbers more than 10,400 (Väisänen et al. 2011, Ottosson et al. 2012). It is surmised that the Fennoscandian birds moult in highly productive wetlands in Russia (Beekman 1998), most likely in the Arkhangelsk Region (Boiko & Kampe-Persson 2012) but, except for one Finnish bird found moulting on the Kanin Peninsula (Litvin & Gurtovaya 2003) and three Latvian birds found moulting in the Arkhangelsk Region (Boiko & Kampe-Persson 2012), concrete evidence is lacking (Fransson & Pettersson 2001, Valkama et al. 2012). In the Baltic States and Poland, on the other hand, there is at least one moulting site for more than 20 individuals in each country (Luigujõe et al. 2002, Boiko 2008, Wieloch & Sikora 2008, Morkūnas et al. 2010). Non-breeding Whooper Swans that moult in the Baltic States may be birds unable to undertake a