Effects of reduced grazing on population density and breeding success of black grouse in northern England

Abstract

Summary 1.The maintenance or modification of grazing regimes is frequently advocated to deliver conservation targets in pastoral landscapes, but there are few quantitative studies of the effects of grazing on upland birds. This is particularly true with respect to grazing management in agri-environment schemes. 2. Numbers of black grouse Tetrao tetrix and their breeding success were therefore monitored at 20 sites in the north of England from 1996 to 2000. Ten treatment sites included areas where grazing was reduced before and during the study to < 1·1 sheep ha − 1 in summer and < 0·5 sheep ha − 1 in winter. Each was paired with a reference site that held sheep at two (summer) to three times (winter) the density on the experimental sites. The reduced grazing sites ranged from 0·4 to 3·2 km 2 in size and most were part of existing agreements within agri-environment schemes that had been in place for 1-5 years before 1996. 3. Numbers of black grouse males displaying increased by an average of 4·6% (SE = 2·1) year − 1 at the 10 sites with reduced grazing. Displaying male trends differed significantly between treatment and normally grazed reference sites, where numbers declined annually on average by 1·7% (SE = 1·4). 4. Summer black grouse hen densities showed the greatest rate of increase where grazing was restricted on smaller areas of ground (0·4 km 2 ). Declines occurred at sites where the area of restricted grazing exceeded about 1 km 2 . The rates of change in population density, as indicated by numbers of displaying males, peaked in the early years of grazing reduction and then declined after c. 5-7 years. 5. The proportion of females that retained broods during the late chick-rearing period was 54% (SE = 0·06) at sites with reduced grazing, significantly greater than the 32% (SE = 0·06) at normally grazed reference sites. There was no difference in the size of broods between grazing treatments. 6. This study demonstrates that agri-environment schemes, which encourage extensive management of grazing land, can benefit at least some organisms of conservation importance and lead to some recovery of populations. There is a need, however, for further understanding of how such benefits can be maintained at a landscape scale and over the greater time scales involved in vegetation dynamics and bird population processes.

Declining reproductive output in capercaillie and black grouse – 16 countries and 80 years

“…Lower biodiversity might be a consequence of reduced grazing pressure as well as negative impacts on the trade-offs between cover and food-searching that brood-rearing hens exhibit (Signorell et al, 2010). By contrast, in Britain, over-grazing by both red deer (Cervus elaphus) and domestic sheep (Ovis aries) is associated with lower densities of black grouse, lower insect abundance and reduce black grouse reproduction (Baines, 1996;Calladine et al, 2002).…”

The recent declines of farmland bird populations in Britain: an appraisal of causal factors and conservation actions

“…3; Baines & Hudson 1995, Baines 1996, Jenkins & Watson 2001. Local populations responded, with improved breeding success and breeding densities, to reduced grazing within the framework of an agrienvironment scheme, and some also responded in the same way to predator control (Calladine et al 2002, Warren & Baines 2004.…”

Meeting the ecological challenges of agricultural change: editors’ introduction

“…Increasingly, papers published in the Journal of Applied Ecology address the restoration, remediation or repair of a wide range of ecosystem types that have been changed through exploitation (Ormerod 2003b). Many such studies apply directly to systems previously altered by agriculture; for example, where extensification has now become an aim, or where moves to encourage or maintain biodiversity within farmed systems have been driven by changing economics or policy ( Wolf et al 2001;Calladine et al 2002;Pywell et al 2002Pywell et al , 2003Middleton 2003;Pretty et al 2003;Smith et al 2002Smith et al , 2003. Across those areas of Europe and the world where agrienvironment schemes are developing, methods for restoring land after cultivation, for protecting adjacent systems such as wetlands, or for maintaining nature conservation interest during cultivation, must from here on respond to factors linked to GM and its associated new technologies.…”