Breeding success of the hen harrier Circus cyaneus in relation to the distribution of grouse moors and the red fox Vulpes vulpes

Abstract

Summary 1. A recent analysis showed that the survival and breeding success of female hen harriers were much lower on grouse moors than on other upland land management classes in Scotland, excluding the Orkney islands: a difference attributed to persecution of hen harriers by humans on grouse moors. However, this study did not look for possible beneficial effects on hen harrier breeding success of the control by moorland gamekeepers of other predators, particularly red foxes. 2. These and other recently published data were re‐examined to see whether there was regional variation in hen harrier nest success associated with the presence or absence of foxes and the control of foxes and other predators by moorland gamekeepers. 3. The main finding of the previous analysis, that nest success was much lower on grouse moors than on moorland that was not managed for grouse or in young conifer forests, was even more striking when comparisons were made among land management classes within the same region. 4. The mean number of broods fledged per female hen harrier per year on two grouse moors at which gamekeepers prevented human interference with harrier nests and continued to control other predators was compared with the average for moorland in Scotland. Harrier productivity on these moors was much higher than the average for grouse moors, but similar to the average for moorland not managed for grouse shooting. 5. Nest success of hen harriers breeding on moorland not managed for grouse averaged 19% higher in regions where there were, on average, more grouse moors in the vicinity, but in young conifer forests success was 34% lower in regions with more grouse moors nearby. Neither of these differences was statistically significant. 6. Nest success within a particular land management class was not significantly different inside and outside the range of the red fox. 7. Even a generous assessment of the magnitude of a supposed beneficial effect of the control of foxes and other predators by moorland gamekeepers on hen harrier nest success indicated that its effect on the population trend of hen harriers would be small relative to the large negative effect of persecution of harriers on grouse moors.