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Providing evidence to improve practice

Action: Control mammalian predators on islands for waders Bird Conservation

Key messages

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  • A controlled before-and-after study in New Zealand found that the Chatham Island oystercatcher Haematopus chathamensis population increased following the removal of feral cats Felis catus and other species.
  • A second controlled before-and-after study in Alaska, USA, found small increases in black oystercatcher Haematopus bachmani breeding populations on two islands, but the overall population only increased on one, declining on the other.


Supporting evidence from individual studies


A controlled before-and-after on Simeonof (4,000 ha) and Chernabura (3,000 ha) Islands in the Shumagin Islands, Alaska (Byrd et al. 1997), found that the probable breeding populations of black oystercatchers Haematopus bachmani increased following the eradication of introduced arctic foxes Alopex lagopus (Simeonof: four pairs in 1994 vs. five in 1995; Chernabura: three and five pairs). Total estimated population increased on Simeonof (34 to 41 birds) but decreased on Chernabura (25 to 19 birds). Oystercatcher densities were significantly lower than on islands without foxes.



A controlled before-and-after study on Chatham Island (899 km2), New Zealand between 1999 and 2005 (Moore 2005) found that the number of Chatham Island oystercatchers Haematopus chathamensis breeding in a 14 km stretch of beach increased from 16 to 35 pairs over the study period, following the initiation of control (trapping and shooting) of predators, principally feral cats Felis catus, but also other introduced mammals and weka Gallirallus australis. Birds in the management area fledged 18-35 chicks/year, compared with very low fledging success in unmanaged areas.


Referenced papers

Please cite as:

Williams, D.R., Child, M.F., Dicks, L.V., Ockendon, N., Pople, R.G., Showler, D.A., Walsh, J.C., zu Ermgassen, E.K.H.J. & Sutherland, W.J. (2019) Bird Conservation. Pages 141-290 in: W.J. Sutherland, L.V. Dicks, N. Ockendon, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2019. Open Book Publishers, Cambridge, UK.