Causes of change

There is little good evidence available regarding the drivers of the breeding population increase in this species in the UK.

Further information on causes of change

Information about demographic trends is very sparse for this species and there is very little evidence generally relating to the causes of the population increases in the UK.

Mallards originating from domesticated birds and not resembling wild-type birds in either plumage or behaviour are very abundant but perhaps under-represented in survey data, especially since many individuals might appear to be semi-captive. A large part of the increase in breeding numbers may be attributable to such birds, rather than to true-bred stock. It is also likely that increases may be at least partly attributable to ongoing large-scale releases for shooting (Marchant et al. 1990). In a study in central France, Champagnon et al. (2016), found that overall survival rate of released birds was low, and equivalent to half the first-year survival of wild Mallards in the same area. Nonetheless, they estimated that a minimum of 34% of the Mallards in the region at the start of the next breeding season were of captive origin.

Declines in wintering numbers have been linked to a decrease in continental immigration (Mitchell et al. 2002, Sauter et al. 2010). The effects of ingested lead gunshot has also been identified as a possible cause of declines in wintering numbers. Analysis of the trends for eight duck species, including Mallard, identified a significant negative correlation between levels of ingested lead gunshot and population changes, and did not find any evidence to support a link to decreased immigration (Green & Pain 2016 1990). Guillemain et al. (2010) found trends of increasing average body mass of Mallard in France which were large enough to have major fitness consequences with respect to winter survival, suggesting that overwinter survival has not decreased. Overwinter loss was investigated in Mallard at 35 inland waters in the Midlands and southern England (Hill 1984). Duckling mortality was the key factor, explaining 58% of total mortality between years and this was weakly density dependent. Overwinter loss was higher following years when a large number of young were produced and was the main regulatory factor.

Information about conservation actions

The recent breeding trend for this species has been relatively stable following previous increases although the wintering numbers have been declining since the 1980s. As for other wetland species ongoing local site management actions to maintain favourable conservation status are likely to support the Mallard. These might include the creation of new wetland habitats such as gravel pits, the creation of nesting sites such as islands and the ongoing management of existing habitats through ensuring that water quality is monitored, and that suitable good quality wetland habitat is maintained.

Whilst site management will provide nesting habitat at individual sites, landscape scale approaches which plan management activity and the creation of a network of sites over a wider area can lead to a greater-than-proportional increase in Mallard abundance (Newbold & Eadie 2004). Therefore, policies which encourage a landscape scale approach to wetland creation and management should be preferred.

The spread of domesticated birds into the wild breeding population could be a potential threat to this species as it may lead to hybridization and a loss of pure native stock, and large numbers of birds descended from domestic stock may already be present in the wild in Europe ( Cizkova et al. 2012). It is unclear what action can be taken apart from attempting to prevent new introductions wherever possible, as it is not always straightforward to recognise hybrids (Simberloff 1996).

Habitat creation and management is also likely to benefit wintering Mallards. Declines in wintering numbers have been attributed to a decrease in immigration from the continent, with birds tending to winter further north and east as a result of climate change (Mitchell et al. 2012; Sauter et al. 2010), with the effects of ingested lead gunshot another possible contributory factor. Conservation actions and policies to encourage shooters to replace lead gunshot with alternatives are therefore another measure which may help to reduce the UK decline (Green & Pain 2016). The provision of refuges from hunting may also help wintering Mallards (Evans & Day 2002). If the main driver of change is changing migration patterns, these actions may only slow the UK decline rather than reversing it, but will also help to ensure that the European breeding population is maintained.