Original Article

Journal of Ornithology

, Volume 147, Issue 3, pp 405-413

First online:

Nocturnal foraging by great skuas Stercorarius skua: implications for conservation of storm-petrel populations

  • Stephen C. VotierAffiliated withMarine Biology and Ecology Research Centre, School of Biological Sciences, University of Plymouth Email author 
  • , Jonathan E. CraneAffiliated withInstitute of Biomedical and Life Sciences, Graham Kerr Building, University of Glasgow
  • , Stuart BearhopAffiliated withSchool of Biology and Biochemistry, Medical Biology Centre, Queens University
  • , Ana de LeónAffiliated withInstitute of Biomedical and Life Sciences, Graham Kerr Building, University of Glasgow
  • , Claire A. McSorleyAffiliated withJoint Nature Conservation Committee, Dunnet House
  • , Eduardo MínguezAffiliated withDepartamento de Biología Aplicada, Área de Ecología, Universidad Miguel Hernández. Avda. de la Universidad
  • , Ian P. MitchellAffiliated withJoint Nature Conservation Committee, Dunnet House
  • , Matthew ParsonsAffiliated withJoint Nature Conservation Committee, Dunnet House
  • , Richard A. PhillipsAffiliated withBritish Antarctic Survey, Natural Environment Research Council
    • , Robert W. FurnessAffiliated withInstitute of Biomedical and Life Sciences, Graham Kerr Building, University of Glasgow

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Abstract

At St Kilda, Outer Hebrides, a large colony of great skuas Stercorarius skua feed extensively on one of the largest colonies of Leach’s storm-petrels Oceanodroma leucorhoa in Europe, but little is known about the dynamics of this predator–prey system. Recently published population estimates of storm-petrels make it possible to estimate the impact of skua predation for the first time. Although skuas in the southern hemisphere catch petrels attending breeding colonies at night, it is not known whether congeners in the northern hemisphere also forage during the hours of darkness. We found (using radio-transmitters) that skuas regularly forage at night and (using light intensifying equipment) observed them catching storm-petrels at night. However, skuas also foraged during daylight hours, and it is unknown whether they might also catch storm-petrels at sea. Data on diet composition reveals that the proportion of storm-petrels in skua diet declined between 1996 and 1997, but remained constant thereafter. Although a large proportion of the storm-petrel prey is likely to consist of non-breeders, numbers consumed suggest that breeders and an unknown quantity of transients may also been eaten. The numbers of storm-petrels eaten are not sustainable and may result in substantial long-term population declines. Under current conditions, maintenance of large populations of both Leach’s storm-petrels and great skuas at St Kilda appears to be mutually exclusive.

Keywords

Stercorarius skua Oceanodroma leucorhoa Predator–prey dynamics Conservation Foraging.