Native vertebrate predators can limit the population size of their prey (Messier & Crête 1985; Sinclair et al. 1998). Culling such predators is widely used for protecting domestic stock (Allen & Sparkes 2001) or enhancing game abundance (Potts 1986). The benefits of predator control (PC) for conservation are receiving growing recognition (Gibbons et al. 2007). However, such management can be contentious if predators and prey are valued differently by different stakeholders (Redpath et al. 2004) and the effects of PC must be properly quantified.
Amongst birds, ground-nesting species are particularly susceptible to predation by avian and mammalian predators and negative impacts of predation have been recorded for gamebirds and waterfowl on incubating adults, eggs and chicks (Marcström, Kenward & Engren 1988; Newton 1993). The effects of predators on populations of other ground-nesting species such as waders (Charadriiformes) are less well studied (Hill 1988; Bolton et al. 2007), although predators are known to have a substantial impact on their breeding success (Baines 1990; Grant et al. 1999).
Generalist predators such as foxes and carrion crows have increased markedly in the United Kingdom in recent decades (Tapper 1992; Gregory & Marchant 1996), associated with increased food availability and declines in the number of gamekeepers (Hudson 1995; Fuller & Gough 1999). The impact of increasing predator numbers on prey populations may be exacerbated when coupled with habitat deterioration, which can increase a prey species’ susceptibility to predation (Baines 1990; Evans 2004). There is, however, a need to quantify the benefits of PC on target species in isolation from variation in habitat quality.
Heather Calluna vulgaris (L.) dominated moorland in the uplands of the United Kingdom is of high international conservation importance for a range of bird species (Thompson et al. 1995). Breeding lapwing Vanellus vanellus (L.) and curlew Numenius arquata (L.) have shown widespread population declines in these areas over the last 20 years (Sim et al. 2005). PC is a well-established management technique across large areas of heather moorland managed for red grouse Lagopus lagopus scoticus (Latham) shooting, thus providing an ideal system in which to test whether PC benefits other ground-nesting birds. The predators controlled are primarily foxes Vulpes vulpes (L.) and carrion crows Corvus corone (L.), which combined with rotational strip burning of heather and management of grouse parasites, maximizes the number of red grouse (Hudson & Newborn 1995). In addition to legal PC, illegal killing of birds of prey still occurs on some moors (Etheridge, Summers & Green 1997).
We conducted a large-scale field experiment where foxes, crows, stoats Mustela ermina (L.) and weasels M. nivalis (L.) were controlled to examine responses in bird breeding success and breeding numbers.