Long-term trends in abundance and breeding success of red grouse and hen harriers in relation to changing management of a Scottish grouse moor

摘要

Large areas of heather moorland in the British uplands are managed for shooting red grouse Lagopus lagopus scotica. However, there has been a long-standing conflict between grouse moor management and the conservation of raptors, particularly the hen harrier Circus cyaneus. Langholm Moor, a grouse moor in southwest Scotland, has hosted studies aiming to resolve this conflict for 24 years. Between 1992 and 1997, whilst managed as a grouse moor, hen harrier numbers increased from two to 20 breeding females, and raptor predation removed large proportions of both adult grouse and chicks. As driven shooting was no longer viable, grouse moor management ceased in 1999, and was not restored until 2008. This paper considers how cessation and subsequent restoration of grouse moor management, which involved heather management and legal control of generalist predators, affected the abundance and breeding success of red grouse and hen harrier, as well as the abundance of their perceived key predators; red fox Vulpes vulpes and carrion crow Corvus corone. Grouse moor management had a positive effect on abundance and breeding success of grouse and harriers, which were two- to three-fold higher when fox indices and crow abundance were reduced by 50–70%. Fox indices were negatively correlated with red grouse density and harrier breeding success, whereas crows were negatively correlated with grouse breeding success. This study confirms that both grouse and harriers can benefit from grouse moor management, if harriers are not persecuted. However, restoration of grouse moor management, in combination with diversionary feeding of harriers, has not yet resulted in a sufficiently increased grouse density to allow driven shooting on Langholm Moor, and thus the management to be considered as economically viable.