Evidence for food limitation in the declining hen harrier population on the Orkney Islands, Scotland

A Amar, S Redpath, S Thirgood

Research output: Contribution to journalArticle

30 Citations (Scopus)

Abstract

The hen harrier (Circus cyaneus) population on the Scottish Orkney Islands has declined dramatically since the end of the 1970s. We postulate that the cause of this decline was due to a reduction in the amount of available prey and predict that if this was the case the population would currently be limited by food. The evidence for this hypothesis is explored by examining the rates at which males deliver prey to their females in relation to breeding performance both among individuals within the declining population and also between this declining population and another, non-declining population in southern Scotland. Breeding performance within the Orkney population was related to male provisioning rates: males that provided more food to their females were more likely to initiate a breeding attempt and there was a tendency for males with the highest provisioning rates to breed with more females. Comparisons between the two populations revealed that harriers on Orkney had a lower breeding performance and also a lower rate of food provision. Changes in agriculture, in particular decreases in rough grazing and increases in sheep densities are thought to be the most likely cause for a reduction in food supply. Conservation measures should be aimed toward increasing the areas of rough grass habitat. (C) 2003 Elsevier Science Ltd. All rights reserved.

Original languageEnglish
Pages (from-to)377-384
Number of pages8
JournalBiological Conservation
Volume111
Publication statusPublished - 2003

Keywords

  • declining population
  • conservation
  • hen harrier
  • breeding success
  • Orkney
  • provisioning rates
  • raptor
  • polygyny
  • food limitation
  • CIRCUS-C-CYANEUS
  • BIRD POPULATIONS
  • SEX-RATIO
  • LAND-USE
  • SURVIVAL
  • POLYGYNY
  • BIOLOGY
  • GROUSE
  • VOLES

Cite this

Evidence for food limitation in the declining hen harrier population on the Orkney Islands, Scotland. / Amar, A ; Redpath, S ; Thirgood, S .

In: Biological Conservation, Vol. 111, 2003, p. 377-384.

Research output: Contribution to journalArticle

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AB - The hen harrier (Circus cyaneus) population on the Scottish Orkney Islands has declined dramatically since the end of the 1970s. We postulate that the cause of this decline was due to a reduction in the amount of available prey and predict that if this was the case the population would currently be limited by food. The evidence for this hypothesis is explored by examining the rates at which males deliver prey to their females in relation to breeding performance both among individuals within the declining population and also between this declining population and another, non-declining population in southern Scotland. Breeding performance within the Orkney population was related to male provisioning rates: males that provided more food to their females were more likely to initiate a breeding attempt and there was a tendency for males with the highest provisioning rates to breed with more females. Comparisons between the two populations revealed that harriers on Orkney had a lower breeding performance and also a lower rate of food provision. Changes in agriculture, in particular decreases in rough grazing and increases in sheep densities are thought to be the most likely cause for a reduction in food supply. Conservation measures should be aimed toward increasing the areas of rough grass habitat. (C) 2003 Elsevier Science Ltd. All rights reserved.

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