Causes of change

There is good evidence to support the hypothesis that the primary demographic driver of Turtle Dove declines is a shortened breeding period, which has reduced the number of nesting attempts. This is thought to be driven by reduced food availability due to increased herbicide use, although analyses that test this directly are lacking. Note, however, that data do not permit analyses of variation in annual survival rates, but mortality both on the wintering grounds (due to habitat deterioration) and on migration (particularly through hunting) could be important.

Further information on causes of change

A four-year intensive field study in East Anglia provided good evidence that the role of breeding productivity in the decline of Turtle Doves is likely to be through a reduction in the average number of nesting attempts per pair (Browne & Aebischer 2005). Browne & Aebischer (2003a, 2004, 2005) concluded that Turtle Doves today have a substantially earlier close to the breeding season and consequently produce fewer clutches and young per pair than they did in the 1960s. Reduced food availability due to increased herbicide use and efficacy may make birds more likely to cease breeding earlier than during the 1960s and reduce their number of nesting attempts (Browne & Aebischer 2001, 2002), although this was not specifically tested. Browne & Aebischer (2003a) state that it may be a change in phenology of Turtle Doves and their food species which has resulted in reduced availability of food supplies, although they do not support this with any specific analyses of these two factors. More recent work, using DNA analysis to assess food items consumed by nestlings, found that those in better condition were fed on a higher proportion of natural arable plant seeds rather than seed from anthropogenically grown sources such as brassicas (Dunn et al. 2018).

Loss of quality and quantity of breeding habitat are also thought to contribute to declines. Browne et al. (2004) used long-term CBC data to provide good evidence that breeding density fell in proportion to loss of nesting, rather than feeding, habitat and that changes in Turtle Dove density were positively related to changes in the amount of hedgerow and woodland edge. Dunn & Morris (2012) suggest however that, although established scrub and large hedgerows were important in retaining Turtle Dove territories, it may be foraging habitat that is limiting their distribution. A small sample (15) of fledglings tracked using radio tags were found to remain close to the nest for the first three weeks, and select seed-rich habitats on foraging trips, and heavier birds were more likely to survive, suggesting nearby foraging habitat was important both pre- and post-fledging (Dunn et al. 2016). Recent research has also investigated customized management options which might provide foraging habitat for Turtle Doves (Dunn et al. 2015).

There is good evidence to suggest that the population decline experienced by Turtle Doves breeding in Britain is not due to lower success of individual nesting attempts. Analysis of nest record cards and ringing data for farmland Turtle Doves shows a non-significant increase in productivity per nesting attempt while annual survival has fallen (Siriwardena et al. 2000a, 2000b, Browne et al. 2005) so this may have also contributed to the decline. The demographic trends shown here support the view that nesting success per attempt is not the main driver of population change, with no significant changes identified in any of the measures (see above).

Turtle Dove is a quarry species in many European countries and Vickery et al. (2014) estimate that 2-4 million Turtle Doves are shot annually in southern Europe. Hunting during migration has been cited as another possible cause of the UK decline, although there is little evidence to support this (Browne & Aebischer 2004). A recent study concluded that the current levels of legal hunting in Europe are more than double the sustainable hunting rate (Lormee et al. 2019), but it is not clear how many birds originating from Britain might potentially be affected by hunting. Ring-recovery sample sizes are small and there is only weak evidence suggesting a decrease in annual survival (Siriwardena et al. 2000b). Nevertheless, survival could also have been negatively affected by a reduction in the quality of wintering habitat: this is thought to have contributed to the decline (Marchant et al. 1990) and one recent study has demonstrated a positive correlation between survival rate among breeding adults in France and food supply in West Africa, as measured by cereal production (Eraud et al. 2009). Further work on the ecology of Turtle Doves on their wintering grounds is needed to investigate the relevance of this result for UK birds. Trichomonosis, a disease widespread since 2005 that reduces fitness and survival among pigeons and other birds, has been recently observed in Turtle Doves and might therefore be a new factor in its decline (Stockdale et al. 2015).

Information about conservation actions

The most important driver of decline in the UK is believed to be a reduction in the number of breeding attempts due to low natural arable plant seed availability as a result of herbicide use. Hence actions designed to provide suitable nesting and foraging habitat are required (Browne & Aebischer 2004; Dunn & Morris 2012), particularly those that provide sufficient abundance of natural seeds throughout the breeding season (Browne & Aebischer 2003b; Dunn et al. 2016). Specific management actions might include the provision of uncropped margin or plots or set-aside, planting buffer strips around arable fields, sowing wild bird seed mixes, restoring or creating semi-natural grassland and managing hedgerows to provide nesting opportunities.

The decline has been so severe that the future of this species is precarious at a national level. Therefore, the provision of agri-environment options which pay farmers in and near the remaining strongholds for this species may be critical to encourage and enable the local habitat management actions described above: prompt and targeted action may be required to save this species as a UK breeding bird. In addition, supplementary feeding has been suggested as a potential action which could improve breeding productivity for this species; a field experiment did not find a significant positive effect from supplementary feeding, although the authors believed that the experimental sites were too small to show such an effect as Turtle Doves range widely during the breeding season (Browne & Aebischer 2002).