Effects of feral mink removal on seabirds, waders and passerines on small islands in the Baltic Sea Mikael Nordstro¨m a, *, Jouko Ho¨gmander b , Jarmo Laine c , Jukka Nummelin c , Nikolaj Laanetu d , Erkki Korpima¨ki a a Department of Biology, Section of Ecology, University of Turku, FIN-20014 Turku, Finland b Metsa ¨hallitus—Forest and Park Service, Natural Heritage Services, Southern Finland, FIN-21660 Nauvo, Finland c Bureau of Environment, City of Turku, Linnankatu 61, FIN-20100 Turku, Finland d Kalevi 69-1, EE-Tartu 50 103, Estonia Received 24 January 2002; received in revised form 10 April 2002; accepted 29 April 2002 Abstract We studied the effects of removing introduced American mink (Mustela vison) on the number of birds breeding on small islands in the Baltic Sea. During autumn 1992–2001 mink were removed from a 72 km 2 area, while mink were not removed from a 35 km 2 control area. Second removal (125 km 2 ) and control areas (130 km 2 ) were established during 1998–2001. The breeding densities of ringed plover (Charadrius hiaticula), arctic skua (Stercorarius parasiticus), arctic tern (Sterna paradisaea) and rock pipit (Anthus petrosus) increased markedly in the removal areas in comparison to the control areas. Turnstone (Arenaria interpres), common gull (Larus canus) and wheatear (Oenanthe oenanthe) also appeared to increase. Two species already extinct in one of the removal areas, razorbill (Alca torda) and black guillemot (Cepphus grylle), returned to breed in the area. Breeding densities of great black-backed gull (Larus marinus), oystercatcher (Haematopus ostralegus) and white wagtail (Motacilla alba) were unaffected. We conclude that it is possible to remove feral mink from large archipelagos with many small islands, and that mink removal increases the breeding densities of many bird species in this habitat. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Biodiversity in archipelago; Breeding densities of birds; Feral mink management; Introduced predator; Mustela vison 1. Introduction Predation by introduced species on native fauna has caused considerable devastation in the global biodi- versity via dramatic reductions in prey populations (Atkinson, 1996; Williamson, 1996; Bright, 1998; Man- chester and Bullock, 2000). Lack of coevolution has certainly contributed to the overwhelming effects that introduced predators have had on their prey (Savidge, 1987; Fritts and Rodda, 1998; Short et al., 2002). Introduced predators are considered to be one of the most important threats to seabird and endemic bird populations, particularly for seabirds breeding on iso- lated small islands (Atkinson, 1996; Tucker and Evans, 1997; Martin et al. 2000; Dowding and Murphy, 2001). Control programmes to manage introduced predators have often turned out to be inconvenient and insuffi- cient (Coˆte´ and Sutherland, 1997). American mink (Mustela vison) were brought to Eur- ope for fur-farming in the 1920s (Dunstone, 1993). In Finland, escaped animals from fur farms started to spread in the 1950s and by the 1970s the species had spread all over the country (Kauhala, 1998). American mink is a semi-aquatic, generalist predator and its main food consists of fish, birds (eggs, nestlings as well as adults), small mammals and amphibians. Birds con- stitute a large part of its diet during spring and summer (Gerell, 1967; Dunstone and Birks, 1987; Niemimaa and Pokki, 1990). Predation by feral American mink is thought to have led to local declines in a wide range of sea and wetland bird species throughout North Europe and the British Isles (e.g. Andersson, 1992; Kilpi, 1995; Craik, 1997; Ferreras and Macdonald, 1999; Hario, 2000; Nordstro¨m et al., 2002). Birds breeding on small islands in the Baltic Sea had not generally been in touch 0006-3207/03/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0006-3207(02)00162-3 Biological Conservation 109 (2003) 359–368 www.elsevier.com/locate/biocon * Corresponding author. Fax: +358-2-3336550. E-mail address: miknor@utu.fi (M. Nordstro¨m).