Causes of change

At present, the link between potential factors and the population trend of Kestrels has not been established and new research is needed. In the meantime, landowners keen to offer suitable Kestrel habitat should provide grassy cover for small mammals.

Further information on causes of change

The main period of decline in Britain occurred from the mid 1970s to the late 1980s and it has been linked to the effects of agricultural intensification on farmland habitats and their populations of small mammals (Gibbons et al. 1993), but it is interesting to notice that the number of nestlings fledged per breeding attempt had not declined, suggesting that, in areas retaining Kestrels, small mammals were not limiting fledging success. Integrated analyses suggest that changes in first-year and, particularly, adult survival are the primary contributors to population change (Robinson et al. 2014). Modelling suggests that climate change may have had a positive impact on the long-term trend for this species, resulting in less negative trends than would have occurred in the absence of climate change (Pearce-Higgins & Crick 2019).

Kestrels hunt a variety of prey, including voles, in particular in farmland settings (Shrubb 1993). Field voles Microtus agrestis favour habitats that can provide dense, grassy cover and a thick litter layer (Hansson 1977). Their population fluctuates in four-year cycles and it has been suggested that this might affect Kestrels that do not switch to other prey such as other small mammals, birds and insects (Shrubb 1993). There is no evidence, however, that Kestrels in the UK fluctuate alongside vole numbers. There is also, at present, no evidence that availability of nest sites limit population size of this raptor. A study over 23 years in a coniferous forest in northern England found a negative relationship between the numbers of Kestrels and Goshawks Accipiter gentilis, and remains of the smaller species near Goshawk nests (Petty et al. 2003). The impact of this larger raptor on population trend of Kestrels is not clear at the national level; however, it may be a factor at a local scale and more studies should focus on predation on Kestrels by other raptors.

Species high in the food chain are at risk of secondary poisoning, and birds of prey feeding on rodents are particularly vulnerable to anticoagulant rodenticides, but these are not the main cause of mortality of Kestrel in the UK (Walker et al. 2013) nor abroad (Christensen et al. 2012). A study on causes of death in raptors showed that the majority of Kestrels had died from collision and starvation (Newton et al. 1999). Carcasses reported for toxicology might be biased towards certain circumstances of death (eg collisions with vehicles) and could therefore underestimate the impact of rodenticides on Kestrel and other birds of prey. Targeted studies should be carried out, ideally to collect samples from live birds as well as dead ones.

Declining population of Kestrel is likely to be due to multiple factors. Changes in agricultural practice have reduced the habitat for its prey species, such as voles (although population trends of small mammals are not easy to establish (Flowerdew et al. 2004, Macdonald et al. 2007). Small rodents are abundant in road verges which provide suitable habitat for these mammals (Bellamy et al. 2000). In turn, Kestrel may be drawn to hunting along roads with increased risks of collision with passing vehicles, although there is no evidence for this at present. More research is needed to establish links between potential factors and Kestrel population change. In the meantime, landowners keen to offer suitable Kestrel habitat should provide grassy cover for small mammals.

Information about conservation actions

At present the link between potential factors and the population trend of Kestrel has not been established and new research is needed. In the meantime, landowners keen to offer suitable kestrel habitat should provide grassy cover for small mammals. Conservation policies can encourage the provision of suitable habitat at a landscape scale by enabling the take-up of agri-environment options such as buffer strips, uncultivated margins, conservation headlands and set-aside.

It should be noted, however, that kestrels do not use buffer strips or similar habitats directly but prefer to hunt over recently mown grassland adjacent to buffer strips where they can more easily catch mammals moving from the longer grass (Aschwanden et al. 2005; Garratt et al. 2011). Therefore, landowners (and agri-environment schemes) should aim to provide a mosaic which includes areas of recently cut grass adjacent to the mammal habitats.

Anticoagulant rodenticides (rat poisons) have been found in some Kestrel carcasses in the UK, with large concentrations found in some birds but no clear evidence that they were a contributory cause of death (Walker et al. 2013). Nevertheless, precautions such as prompt removal and safe disposal of poisoned rates, as well as continued monitoring, would be prudent.