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Providing evidence to improve practice

Individual study: Effects of supplementary feeding on hen harrier Circus cyaneus breeding success on the Orkney Islands, Scotland

Published source details

Amar A. & Redpath S.M. (2002) Determining the cause of hen harrier decline on the Orkney Islands: an experimental test of two hypothesis. Animal Conservation, 5, 21-28


This study is summarised as evidence for the intervention(s) shown on the right. The icon shows which synopsis it is relevant to.

Control predatory mammals and birds (foxes, crows, stoats and weasels) Farmland Conservation

A randomized, replicated, controlled study in 1999-2000 on Orkney Mainland, Scotland (Amar & Redpath 2002) found that the breeding success of hen harriers Circus cyaneus was no different in nine territories where hooded crows Corvus (Corone) cornix were removed, compared to territories without crow removal. The number of clutches/male, clutch size, hatching success and laying date were not affected, although experiments with artificial nests containing chicken eggs showed that predation had been reduced by crow removal (12 of 18 clutches surviving vs two of 18). A total of 113 crows were removed from the nine territories.

 

Provide supplementary food for birds or mammals Farmland Conservation

A randomized, replicated and controlled study in heathland on Orkney Mainland, Scotland, in 1999-2000 (Amar & Redpath 2002) found that male hen harriers Circus cyaneus provided with supplementary food (chicken Gallus domesticus chicks and quarter pieces of European rabbit Oryctolagus cuniculus or brown hare Lepus europaeus) bred with significantly more females than control (unfed) males (100% of 11 fed males mated and 36% mated with more than one female vs 80% of nine unfed males mated, 11% mated with more than one female). There was no effect of feeding on clutch size or hatching success (average of approximately 5.1 eggs/clutch for 13 fed clutches vs 4.7 eggs/clutch for four unfed clutches), but productivity still increased. Hooded crows Corvus cornix were also removed from all territories.

Control avian predators on islands Bird Conservation

A randomised, replicated and controlled study in 1999-2000 on Orkney Mainland, Scotland (Amar & Redpath 2002) found that the breeding success of hen harriers Circus cyaneus was no different in nine territories where hooded crows Corvus cornix (previously Corone cornix) were removed, compared to territories without crow removal. The number of clutches/male, clutch size, hatching success and laying date were not affected, although experiments with artificial nests containing chicken eggs showed that predation had been reduced by crow removal (12 of 18 clutches surviving vs. two of 18). A total of 113 crows were removed from the nine territories. This study is also discussed in ‘Provide supplementary food to increase reproductive success’.

 

Provide supplementary food for raptors to increase reproductive success Bird Conservation

A randomised, replicated and controlled study in heathland on Orkney Mainland, Scotland, in 1999-2000 (Amar & Redpath 2002) found that male hen harriers Circus cyaneus provided with supplementary food (chicken Gallus domesticus chicks and quarter pieces of European rabbit Oryctolagus cuniculus or brown hare Lepus europaeus) bred with significantly more females than control (unfed) males (100% of 11 fed males mated and 36% mated with more than one female vs. 80% of nine  unfed males mated, 11% mated with more than one female). There was no effect of feeding on clutch size or hatching success (average of approximately 5.1 eggs/clutch for 13 fed clutches vs. 4.7 eggs/clutch for four unfed clutches), but productivity still increased. Hooded crows Corvus cornix were also removed from all territories, discussed in ‘Control avian predators on islands’.