Causes of change

The demographic causes of the population increase appear to be an increase in the number of fledglings per breeding attempt, larger brood sizes and a decrease in daily failure rates. However, it is unclear what the ecological drivers of these changes are.

Further information on causes of change

The number of fledglings per breeding attempt has increased strongly, through an increase in brood size and a fall in nest failure rates.

There is little evidence relating to Nuthatch population change in the UK. However, studies from Europe provide evidence that mild winters are likely to have helped this species. Kallander (1997) used a long-term data set (1977-91) to provide good evidence that Nuthatches in a Swedish national park had a population size in spring which co-varied positively with winter temperatures and suggest that increases in population size may be associated with increasing mean winter temperature. Nilsson (1982, 1987) also found that mortality was concentrated in winter and that starvation was probably the major cause. However, a long-term study in Poland from 1975 to 1990 found that bird numbers in spring were not significantly correlated with the severity of the preceding winter, though winter survival was higher in the unusually mild winter of 1989/90, which had a rich supply of hornbeam seeds (Wesolowski & Stawarczyk 1991). It is not possible to say whether such factors have also operated in the UK, as the climate here is considerably less extreme.

Several studies have also reported a link between population size and the size of food availability in the autumn. A study of two Nuthatch populations in Sweden provided good evidence that autumn population size was correlated with the size of the hazelnut crop, suggesting food supplies play a role, although beechmast crop was not correlated with overwinter survival and nor was autumn population size correlated with the population density in spring (Enoksson & Nilsson 1983, Enoksson 1990). In the studies by Nilsson mentioned above, the main density-dependent factor, recruitment of young of the year to the autumn population, was positively related to the current beechmast supply and negatively to the density of adults (Nilsson 1982, 1987). A long-term study in Poland from 1975 to 1990 also found that Nuthatch numbers seemed to be influenced by autumn seed supply and also availability of caterpillars in the preceding spring (Wesolowski & Stawarczyk 1991). Another continental study in Europe found that local survival in autumn was higher in beechmast years for juveniles, but not for adults and that local winter survival was not higher in years with than in years without beechmast (Matthysen 1989). Thus there is some evidence that increases in population size are linked to food supplies, but again, this has not been directly tested for UK birds.

Although there is no direct evidence available, Nuthatches are known to favour dead wood, and so it is possible that they may have benefited from the increase in dead wood in the UK (Amar et al. 2010a).

In Belgium, competition for nest sites with the non-native, invasive Ring-necked Parakeet was found to be detrimental to Nuthatches (Strubbe & Matthysen 2009). However, there is evidence showing that this is not a problem in the UK at present (Newson et al. 2011).

Information about conservation actions

The population of this species has increased consistently since the 1970s and it has expanded its range northwards, hence it is not a species of concern and no conservation actions are currently required.

Conservation actions benefiting other woodland species may also help Nuthatch. Habitat fragmentation may prevent Nuthatches from finding new sites (Verboom et al. 1991; Bellamy et al. 1998; van Langevelde 2008), and the provision of more frequent suitable patches of woodland across the landscape may therefore enable further colonisation and range expansion. Fragmentation may explain why numbers are relatively low and there are gaps in distribution in eastern England (Bellamy et al. 1998).