Causes of change

The causes of change are uncertain although it is likely that reduced survival drove the initial declines. Agricultural intensification may have contributed to the decline in farmland, but other factors probably operated in woodland and urban habitats.

Further information on causes of change

CBC results show that the decline began in the mid 1970s. It is likely that reduced survival drove the decline (Siriwardena et al. 1998a), although there has been little overall change in survival as recorded by CES since 1983. Adult survival in an intensive colour-ringing study was lowest in the spring during the early breeding season and highest during the autumn (Robinson et al. 2010a); the survival rates found by this study were similar to those found by an earlier study in the 1970s (Batten 1978). However, the 2010 study covered a small geographical area and the survival rates from this area may not be representative of the whole of the UK. Subsequent demographic analysis of national data indicates that annual population changes actually correlate best with adult survival, although population processes appear to differ between eastern and western Britain (Robinson et al. 2012). Fledgling numbers per breeding attempt increased during the population decline and are now decreasing again, suggesting that productivity is density-dependent. Agricultural intensification is likely to have contributed to the population decline (Fuller et al. 1995) but, since numbers fell in woodland as well as farmland, additional factors probably operated. Analysis of nest record data suggests that different factors may affect nest survival in urban and countryside habitats, and that nest productivity is higher in intermediate (urban rural) habitats (Miller et al. 2017).

Information about conservation actions

The causes of the decline from the 1970s to the mid-1990s are uncertain and hence it is also unclear which conservation actions will be most likely to help reverse the declines. Blackbird numbers did increase from the late 1990s until around 2010, suggesting that the earlier issues may no longer be occurring, but these increases have stalled and numbers remain substantially lower than in the late 1960s.

Decreases in farmland may relate to agricultural intensification, where conservation actions to support other species may also benefit Blackbird, particularly those that could aid survival as this is suspected to be the main cause of the decline. These could include providing supplementary food over winter, managing hedgerows or woodland habitat for wildlife, and providing additional habitat, e.g. wild bird seed or cover mixtures, set-aside or grass buffer strips/margins. As Blackbird is a partial migrant, local conservation actions to support birds in winter will not necessarily benefit local populations, and changes over a large scale may hence be required in order for conservation actions to have a significant effect on British (and European) populations. During the breeding season, soil moisture can affect breeding success (Miller et al. 2017), and therefore policies that encourage damper soil may benefit Blackbirds, e.g. reduced drainage.

Much of the population of this species lives in woodland and urban areas, where declines have also occurred. Similar conservation actions to try to improve habitats in these areas would be prudent, but further research is needed before specific targeted actions for Blackbird can be proposed.