Causes of change

The decline of the species between the mid 1970s and mid 1980s is likely to be due to several factors, but strong experimental evidence in farmland areas suggests that this may be linked to reduced winter food availability. This reflects similar results found for other species that suffer a 'hungry gap' in February and March.

Further information on causes of change

The cause of the decline between the mid 1970s and mid 1980s is unknown, but a recently constructed integrated population model suggests that variation in adult survival plays a key role in determining annual population change (Robinson et al. 2014). It is possible that decline was limited to the farmland and woodland habitats that were covered by CBC, prior to the inception of BBS in 1994.

Feeding experiments have revealed that the use Dunnocks make of farmland feeding stations peaks after mid February, as natural food becomes depleted, suggesting that food availability on farmland is a limiting factor in the population (Siriwardena et al. 2007, 2008). This reflects similar results found for other farmland birds that experience a 'hungry gap' in February and March (Siriwardena et al. 2008). Evidence from the study also suggested that breeding abundance was stable where the use of provided food was high, although this may be a density-dependent result as high use occurred at high abundance (Siriwardena et al. 2007).

The CBC trend in woodland plots suggested that the species had declined by 58% between 1966 and 2000 (Fuller et al. 2005). The most likely cause for this decline is loss of understorey due to canopy closure, in the absence of forest management and especially to increasing browsing pressure from deer (Gill & Fuller 2007). In Bradfield Woods, Suffolk, Dunnocks responded negatively to browsing pressure (Holt et al. 2011). Shrub density has been identified as the most important predictor of Dunnock abundance at this site (Fuller & Henderson 1992).

Information about conservation actions

The most likely driver of the decline of this species on farmland during the late 1970s and 1980s was agricultural intensification and reduced winter food availability. The Dunnock is affected by the 'hunger gap' in late winter (Siriwardena et al. 2008; see Causes of Change section, above) and therefore ensuring food is available after mid-February is likely to be particularly important. Conservation actions and agri-environment options which could help achieve this include supplementary feeding (Siriwardena et al. 2007) and other actions which increase winter food supply such as the planting of wild bird seed cover, the retention of stubble fields, and the use of buffer strips, conservation headlands, set-aside and similar habitats to increase the availability of natural seed resources.

The species is also declining in woodland, where the main cause is likely to be the closure of the canopy and increased levels of deer browsing leading to loss of shrubs in the understorey. Therefore, active woodland management to create a more open canopy and to control deer numbers may create better habitat conditions for Dunnocks.