Raptor predation and population limitation in red grouse

S J Thirgood, S M Redpath, P Rothery, N J Aebischer

Research output: Contribution to journalArticle

99 Citations (Scopus)

Abstract

1. We assessed the impact of predation by hen harriers and peregrine falcons on a red grouse population in southern Scotland during 1992-98. Grouse density in April, July and October declined during this time, coincident with an increase in the numbers of breeding harriers and peregrines.

2. Winter losses of grouse between October and April averaged 33% and were density-dependent. Raptors were the cause of about 70% of winter mortality and they killed about 30% of the grouse present in October. We were unable to determine whether winter mortality in raptors was additive to other losses.

3. Summer losses of adult grouse between April and July averaged 30% and were density-dependent. Raptors were the cause of more than 90% of the early summer mortality of adult grouse. Summer losses of grouse chicks between May and July averaged 45% and were not density-dependent. Harriers killed about 28% of grouse chicks by late July and about 37% by the end of August. Summer raptor predation on adult grouse and chicks appeared to be largely additive to other losses and we estimated that it reduced autumn grouse densities by about 50%.

4. A model combining the estimated reduction in autumn grouse density caused by raptors with the observed density dependence in winter loss predicted that, in the absence of raptors for 2 years, grouse density in spring would be 1.9 times greater, and grouse density in autumn 3.9 times greater, than in the presence of raptors. The model suggested that raptor predation prevented the grouse population from increasing and was thus a limiting factor.

Original languageEnglish
Pages (from-to)504-516
Number of pages13
JournalJournal of Animal Ecology
Volume69
Issue number3
Publication statusPublished - May 2000

Keywords

  • hen harrier
  • peregrine falcon
  • population limitation
  • predation
  • red grouse
  • generalist predators
  • rodent populations
  • Southern Sweden
  • hen harriers
  • survival
  • dynamics
  • growth
  • models
  • cycles
  • impact

Cite this

Thirgood, S. J., Redpath, S. M., Rothery, P., & Aebischer, N. J. (2000). Raptor predation and population limitation in red grouse. Journal of Animal Ecology, 69(3), 504-516.

Raptor predation and population limitation in red grouse. / Thirgood, S J ; Redpath, S M ; Rothery, P ; Aebischer, N J .

In: Journal of Animal Ecology, Vol. 69, No. 3, 05.2000, p. 504-516.

Research output: Contribution to journalArticle

Thirgood, SJ, Redpath, SM, Rothery, P & Aebischer, NJ 2000, 'Raptor predation and population limitation in red grouse', Journal of Animal Ecology, vol. 69, no. 3, pp. 504-516.
Thirgood SJ, Redpath SM, Rothery P, Aebischer NJ. Raptor predation and population limitation in red grouse. Journal of Animal Ecology. 2000 May;69(3):504-516.
Thirgood, S J ; Redpath, S M ; Rothery, P ; Aebischer, N J . / Raptor predation and population limitation in red grouse. In: Journal of Animal Ecology. 2000 ; Vol. 69, No. 3. pp. 504-516.
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N2 - 1. We assessed the impact of predation by hen harriers and peregrine falcons on a red grouse population in southern Scotland during 1992-98. Grouse density in April, July and October declined during this time, coincident with an increase in the numbers of breeding harriers and peregrines.2. Winter losses of grouse between October and April averaged 33% and were density-dependent. Raptors were the cause of about 70% of winter mortality and they killed about 30% of the grouse present in October. We were unable to determine whether winter mortality in raptors was additive to other losses.3. Summer losses of adult grouse between April and July averaged 30% and were density-dependent. Raptors were the cause of more than 90% of the early summer mortality of adult grouse. Summer losses of grouse chicks between May and July averaged 45% and were not density-dependent. Harriers killed about 28% of grouse chicks by late July and about 37% by the end of August. Summer raptor predation on adult grouse and chicks appeared to be largely additive to other losses and we estimated that it reduced autumn grouse densities by about 50%.4. A model combining the estimated reduction in autumn grouse density caused by raptors with the observed density dependence in winter loss predicted that, in the absence of raptors for 2 years, grouse density in spring would be 1.9 times greater, and grouse density in autumn 3.9 times greater, than in the presence of raptors. The model suggested that raptor predation prevented the grouse population from increasing and was thus a limiting factor.

AB - 1. We assessed the impact of predation by hen harriers and peregrine falcons on a red grouse population in southern Scotland during 1992-98. Grouse density in April, July and October declined during this time, coincident with an increase in the numbers of breeding harriers and peregrines.2. Winter losses of grouse between October and April averaged 33% and were density-dependent. Raptors were the cause of about 70% of winter mortality and they killed about 30% of the grouse present in October. We were unable to determine whether winter mortality in raptors was additive to other losses.3. Summer losses of adult grouse between April and July averaged 30% and were density-dependent. Raptors were the cause of more than 90% of the early summer mortality of adult grouse. Summer losses of grouse chicks between May and July averaged 45% and were not density-dependent. Harriers killed about 28% of grouse chicks by late July and about 37% by the end of August. Summer raptor predation on adult grouse and chicks appeared to be largely additive to other losses and we estimated that it reduced autumn grouse densities by about 50%.4. A model combining the estimated reduction in autumn grouse density caused by raptors with the observed density dependence in winter loss predicted that, in the absence of raptors for 2 years, grouse density in spring would be 1.9 times greater, and grouse density in autumn 3.9 times greater, than in the presence of raptors. The model suggested that raptor predation prevented the grouse population from increasing and was thus a limiting factor.

KW - hen harrier

KW - peregrine falcon

KW - population limitation

KW - predation

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KW - generalist predators

KW - rodent populations

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KW - hen harriers

KW - survival

KW - dynamics

KW - growth

KW - models

KW - cycles

KW - impact

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JO - Journal of Animal Ecology

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