Causes of change

The demographic causes of decline are not yet known and, although there is low breeding success in some populations, the reasons for the decline are unclear.

Further information on causes of change

The demographic causes of decline are not yet known, and although there is low breeding success in some populations the reasons for the decline in the UK and elsewhere in Europe are unclear (Charman et al. 2009). A study of nest data in Britain found that the mean number of young fledged has declined since the 1980s, possibly exacerbated by the generally warmer springs, with loss of chicks, probably as a result of starvation, being the main cause of low productivity; hence this could potentially have contributed to the population decline (Smith & Smith 2020). However, a detailed field study in Sweden provided good evidence that neither clutch size, brood size in successful nests, fledging success in successful nests nor mean nestling weight differed significantly there between years, despite a threefold difference in population variation (Wiktander et al. 2001).

Loss of open woodland is one factor that has been suggested to have contributed to declines in this species. Lesser Spotted Woodpecker is a species that requires mature, open woodland and large areas of woodland at a landscape scale (Wiktander et al. 2001, Charman et al. 2010). Wiktander et al. postulate that the decrease in the area of deciduous forest in Sweden is probably one cause of this species' decline, although they present no specific evidence to support this (Wiktander et al. 1992). Loss of dead wood within woodlands has been proposed as another factor; however, given that dead wood has increased in Britain (Amar et al. 2010) this seems an unlikely cause here. A field study in Poland provided evidence that Lesser Spotted Woodpecker presence is closely correlated with the amount of dead wood and large deciduous trees (Angelstam et al. 2002). In their review of the causes of declines of woodland birds Fuller et al. (2005) state that reductions in small-diameter dead wood suitable for foraging may be a factor in the decline, although recent surveys provided evidence that there was no difference in dead-wood abundance between occupied and unoccupied woods (Charman et al. 2010). However, dead snags have a high turnover and were found to be suitable for nesting sites by woodpeckers for only a few years after death and, furthermore, dead-wood conditions may now be more favourable for Great Spotted Woodpeckers (Smith 2007).

A third hypothesis relates to competition and predation. A field study in Sweden found that Great Spotted Woodpeckers compete with Lesser Spotteds for insect food in dead wood when spruce seed crops are low (Nilsson et al. 1992), but evidence for this in Britain is limited (Charman et al. 2010). The two species may compete for nest sites, since they overlap considerably in their use of nesting substrates (Glue & Boswell 1994). Amar et al. (2006) found that Lesser Spotted Woodpecker decreased more heavily in woods with relatively high numbers of grey squirrel dreys but there was no other evidence that squirrel density was a significant factor in declines.

Changing climate has been found to have an impact on survival and reproduction in some populations. In Norway, a positive relationship between spring numbers of Lesser Spotted Woodpecker and previous June temperatures has been interpreted as an effect of temperatures on woodpecker survival and reproduction during the breeding season (Steen et al. 2006, Selas et al. 2008). Steen et al. (2006) also found that winter temperatures exhibit a direct positive effect on winter survival. However, given that there has been a general trend for increasing temperatures in the UK (see here), it seems unlikely that changes in climate have been responsible for Lesser Spotted Woodpecker declines. Work in Sweden and Germany suggests that changes in phenology could play a role in breeding success, finding that declines in food availability during the breeding season are likely to be related to seasonal declines in reproductive performance as woodpeckers adjust their timing of breeding to coincide with the seasonal food peak (Wiktander et al. 2001, Rossmanith et al. 2007). However, there is little further evidence for this. In Britain, breeding success has fallen and is lower than in recent studies in Germany and Sweden; chick mortality is especially high, most probably related to food shortages in the breeding period (Charman et al. 2012, Smith & Charman 2012).

Information about conservation actions

The species requires large areas of mature, open deciduous woodland with deadwood at a landscape scale (Wiktander et al. 2001; Charman et al. 2010), but the decline has occurred even in areas where this habitat has apparently been available. Reasons for the substantial decline of this species remain unclear (see Cause of Change section, above) and investigations are ongoing to try to identify measures that may reverse the downward trend (Smith & Charman 2012).