Determining the cause of the hen harrier decline on the Orkney Islands: an experimental test of two hypotheses

Authors

  • A. Amar,

    Corresponding author
    1. Centre for Ecology and Hydrology, Hill of Brathens, Banchory, Aberdeenshire, AB31 4BW, UK
    2. Department of Zoology, University of Aberdeen, Tillydrone Avenue, Aberdeen, AB24 2TZ, UK
    Search for more papers by this author
  • S. M. Redpath

    1. Centre for Ecology and Hydrology, Hill of Brathens, Banchory, Aberdeenshire, AB31 4BW, UK
    Search for more papers by this author

All correspondence to: Arjun Amar, Game Conservancy Trust, c/o CEH Banchory, Hill of Brathens, Banchory, Aberdeenshire, AB31 4BW, UK. Tel: 01330 826331; Fax: 01330 823303; E-mail: arjuna@ceh.ac.uk

Abstract

A supplementary feeding and predator removal experiment was conducted on the hen harrier population on West Mainland, Orkney, to test whether increased predation pressure or shortage of food was responsible for the poor breeding success and potentially the decline of this population. Although numbers of crows appeared to have increased since 1983, the removal of hooded crows from breeding territories of male harriers had no detectable effect on any of the breeding parameters measured. The provision of supplementary food to male harriers significantly increased their numbers of breeding females, but had no detectable effect on either lay date, clutch size or hatching success. Results suggest that the current low levels of polygyny are a consequence of a shortage of food during the pre-lay period. Conservation management for this species should therefore be directed towards increasing the harriers' food supply, especially during the pre-lay period.

Ancillary