Causes of change

There is good evidence that changes in first-year overwinter survival rates best account for observed population change. Although the ecological drivers of Starling decline are poorly understood, changes in the management of pastoral farmland are thought to be largely responsible.

Further information on causes of change

As the population has dropped, the numbers of fledglings per breeding attempt has increased markedly (see above); clutches are now larger, and rates of nest loss at the egg and chick stage have fallen. These improvements in breeding performance suggest that decreasing survival rates are likely to be responsible for the decline. Evidence for this is provided by Freeman et al. (2007b), who conducted a population modelling exercise and found that changes in first-year overwinter survival rates could best account for observed population change, and were sufficient, on their own, to explain the broad pattern of decline. This pattern is supported by a more recent, integrated, population analysis (Robinson et al. 2014). The decline in survival rates nationwide coincided with the major period of population decline. MacLeod et al. (2008) also provide evidence linking Starling declines to the environmental conditions outside the breeding season, suggesting that the species' population status is dependent on interactive or synergistic effects of food availability and predation. Recent research in The Netherlands has identified changes in juvenile survival as the most likely explanation for similar substantial declines which have affected the Dutch Starling population since the 1990s (Versluijs et al. 2016).

There is little direct evidence from studies analysing the ecological drivers of the declines. However, changes in pastoral farming practices are likely to account for at least some of the decline in the wider countryside, probably related to changes in food resources, though these are largely unquantified (Robinson et al. 2005a). In Denmark, adults selectively forage in grazed areas when feeding nestlings (Heldbjerg et al. 2017), and the decline of the Starling has been linked to changes in grassland area and grazing density (Heldbjerg et al. 2016). A review by Heldbjerg et al. (2019) concluded that cattle abundance was most likely to explain the differences in trends across Europe, rather than grassland extent or temperature. Loss of permanent pasture, which is the species' preferred feeding habitat, and general intensification of livestock rearing are likely to be having adverse effects on rural populations in the UK, but other causes should be sought in urban areas (Robinson et al. 2002, 2005a). Whilst the number of cattle has declined, sheep numbers have increased, producing a different sward structure (Chamberlain et al. 2000b, Fuller & Gough 1999) and patterns of stock rearing have changed. These may have reduced foraging opportunities for Starling (Robinson et al. 2002, 2005a). Also the use of insecticides on grassland, though low, is targeted partly at tipulids, which may have reduced foraging opportunities further (Vickery et al. 2001). Although there is little published evidence that the density of tipulids has changed over time (Wilson et al. 1999), the area of permanent pasture, in which they are mainly found, has declined and the use of insecticides on them has increased. Drainage of grasslands is also thought to have reduced the quality of foraging conditions (Newton 2004). Even after considerable decline among farmland Starlings, tipulids remain important to them for provisioning young (Rhymer et al. 2012).

Suburban habitats important for Starlings with 60% of population in urban/garden habitats but relatively little known about them (Robinson et al. 2005a, 2006), and the causes of declines unclear though nesting attempts produce fewer young than rural birds (Siriwardena & Crick 2002 ). Town populations are doing best in the north and west but declining in the south (Robinson et al. 2005a). Further research into urban Starling population dynamics is to be encouraged if we are to understand the causes of decline of this charismatic species more fully.

Information about conservation actions

In rural areas, changes to pastoral farmland are most likely to be responsible for declines, with the intensification of livestock rearing and loss of permanent pasture reducing foraging opportunities (see Causes of Change section, above). Adults selectively forage in grazed areas when feeding nestlings (Heldebjerg et al. 2017), therefore maintaining grazing at this time is likely to be important. However, as the declines are believed to be driven by reduced first year survival, continued provision of suitable foraging habitat after fledging may be more important. Starlings capture more prey on short swards and providing short swards by grazing or mowing could therefore be a good way to improve foraging habitat (Devereux et al. 2004).

A reduction in the use of insecticides on grasslands may also benefit Starlings by improving foraging opportunities. Although the use of insecticides is low, it is targeted partly at tipulids which are an important prey item for Starlings (see Causes of Change section, above).

Starlings are also declining in urban areas which support around 60% of the population (Robinson et al. 2005a). Urban Starlings produce fewer young than rural birds (Siriwardena & Crick 2002) and urban birds are declining more strongly in the south of Britain than in the north and west (Robinson et al. 2005a). However, the reasons for the decline in urban areas are unclear and further research is needed before evidence-based conservation actions can be proposed.