Field Vole Microtus agrestis abundance and Hen Harrier Circus cyaneus diet and breeding in Scotland

Abstract

In many parts of the global range, voles form an important part of the diet of Hen Harriers Circus cyaneus, and breeding numbers are correlated with the abundance of these small mammals. In Scotland, however, little information is available on harrier diet in the spring and our understanding of causes of variation in harrier breeding density is complicated by human interference. In this paper we explore the relationship between Field Vole Microtus agrestis abundance and harrier spring diet, density and productivity in southern Scotland. Over three years, voles occurred on average in 67% of pellets, and 79% in years of high and intermediate vole abundance. From 1992, the number of breeding harriers increased following protection from illegal persecution. After accounting for this trend, harrier numbers correlated strongly with vole abundance. Harrier clutch size was also correlated with vole abundance. Although fledging success tended to be greater in years of vole increase than in years of vole decline, fledging success was not significantly correlated with the relative abundance of voles, or with the abundance of Meadow Pipits or Red Grouse chicks.

Does timing of breeding matter less where the grass is greener? Seasonal declines in breeding performance differ between regions in an endangered endemic raptor

“…Population dynamics and breeding output of the striped mouse are known to vary strongly with rainfall (see Taylor and Green 1976, Meynard et al 2012, Rymer et al 2013. This, together with our results (relationship between PC2 and both clutch size and productivity), suggests that greater rainfall during autumn and winter could positively influence the abundance of small mammals such as Four-Striped Mouse, which may in turn influence breeding performance in Black Harriers, as found for other species (Korpimäki 1992, Salamolard et al 2000, Redpath et al 2002b. Future studies should investigate the relationship between Black Harrier's breeding and food availability, and how this varies in space and time.…”

Effects of sheep grazing on abundance and predators of field vole (Microtus agrestis) in upland Britain

“…There would also be significant increases in more common bird species such as kestrels and mammals such as stoats and weasels 15 that have undergone declines over recent decades (Gibbons et al, 1993;Harris et al, 1995). Low vole densities in the North Peak may explain why there is only one recent breeding record of the hen harrier, Circus cyaneus a species that selects moorland nesting sites in areas of high field vole density (Redpath et al, 2002), despite the presence of over 135 km 2 of apparently suitable heather moorland. Removing sheep from moorland is beneficial to much biodiversity (Anderson and Yalden, 1981;Dennis, 2003;Fuller and Gough, 1999;Hewson, 1982;Hill et al, 1992) and so promoting suitable vole habitat by reducing grazing ought to satisfy a range of conservation concerns.…”

“…Both density and breeding success of several species of predators have been shown to be strongly related to field vole abundance (e.g. weasel Mustela nivalis (Tapper, 1979), hen harrier Circus cyaneus (Redpath et al, 2002), kestrel Falco tinnunculus (Thirgood et al, 2003;Village, 1982), tawny owl Strix aluco (Petty and Fawkes, 1997), short-eared owl Asio flammeus (Thirgood et al, 2003;Village, 1987), long-eared owl Asio otus (Sundell et al, 2004)). Recent changes in land use in Britain have resulted in an increase in the relative importance of field voles as a prey source for a number of predatory species (Love et al, 2000).…”

Feeding behaviour and diet composition of Marsh Harriers Circus aeruginosus in agricultural landscapes

“…Food supply is one of the main limiting factors for birds of prey. Breeding densities and breeding parameters such as laying date, clutch size or productivity can vary in relation to food availability or diet composition (Newton 1979, Redpath et al 2002, Arroyo & García 2006. Food availability is mainly determined by both the abundance and accessibility of food resources (Preston 1990), which in turn can be affected by changes in the composition and structure of foraging habitats.…”