Causes of change

Demographic modelling provides evidence that a decrease in the annual survival rates of birds in their first year may have driven the decline. The ecological causes of the decline are uncertain as good-quality, direct evidence is sparse.

Further information on causes of change

Nest failure rates show little overall change (with a marginal decrease in egg-stage failure offset by an increase at the chick stage) and the number of fledglings per breeding attempt shows no trend. Though samples are too small to continue presenting a trend, there was a decrease overall in the ratio of juveniles to adults in CES captures. However, demographic modelling shows that decreases in the annual survival rates of birds in their first year of life are more likely to have driven the population decline than breeding parameters (Freeman & Crick 2003, Stevens et al. 2007). This effect on survival may operate in the pre-migration period, during migration or in the wintering quarters. The number of adult Spotted Flycatchers caught at CES ringing sites was found to have declined drastically, providing further evidence that post-fledging and overwinter survival may be important factors in the population decline (Peach et al. 1998).

Evidence for the ecological causes of the decline is sparse. Fuller et al. (2005) hypothesise that declines in large flying insects that are food to the flycatcher, or conditions either on the wintering grounds or along migration routes may be involved. However, there is little detailed evidence to directly support any of these ideas.

Data from the Repeat Woodland Bird Survey (Amar et al. 2006) showed that Spotted Flycatchers were more likely to have declined at sites with very open or very closed foliage conditions. Smart et al. (2007) also suggest this. However, overall, Amar et al. (2006) did not find that changes in habitat were significant in explaining population declines for this species. Stevens et al. (2007) found that nests in gardens fledged twice as many chicks as those in either woodland or farmland. The proximate cause of lower success in farmland and woodland was higher nest predation rates. In a follow-up study using nest cameras, 17 out of 20 predation events were carried out by avian predators and 12 of these were by Jays (Stevens et al. 2008). In terms of nesting success, farmland and woodland appear to be suboptimal when compared with gardens, providing evidence of a problem on the breeding grounds for this species, at least in these two habitats (Stevens et al. 2007). However, the absence of any change in nest failure rates (as reported above) suggests that predation has not been the main driver of the overall decline.

In Leicestershire, Stoate & Szczur (2006) found that the removal of nest predators prompted an increase in Spotted Flycatcher breeding success, especially in woodland, where nest success was lower overall than in gardens. However, Carpenter et al. (2009) found no link between presence/absence, abundance and population change of the species and avian predator abundance.

Information about conservation actions

The ecological drivers of the long-term decline are uncertain, and although there is evidence that it may be linked to first-year survival it is still unclear whether this is occurring during the post-breeding period in the UK, or whilst the species are outside the UK during migration or on their wintering grounds. It is therefore uncertain whether conservation actions taken in the UK will have any significant effect on Spotted Flycatcher abundance.

In woodland, sites with intermediate foliage conditions (rather than very open or very closed foliage) seem to be preferred (see Causes of Change section, above). Nests in woodland or farmland are more likely to be predated than those in gardens (Stevens et al. 2007) and removal of nest predators can lead to localised improvements in breeding success, although there is no evidence that avian predator abundance has population level effects (see Causes of Change section).