§ Baroness Miller of Chilthorne Domerasked Her Majesty's Government:
What increase in the use of slug pellets they have recorded or estimated on (a) farmland, (b) gardens and (c) horticultural holdings over the past 10 years; what is the decline in song thrush population over the same period; and whether they have any evidence of a correlation between the two. [HL1662]
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§ The Parliamentary Under-Secretary of State, Department for Environment, Food and Rural Affairs (Lord Whitty)Pesticide products such as slug pellets are assessed by the Pesticides Safety Directorate for their environmental effects. This includes the evaluation of their toxicity to birds and possible effects on reproduction. Products which are likely to cause a direct and unacceptable impact on the environment do not receive approval for sale or use.
Data are regularly collated and reported on the use of molluscicides for agriculture and horticulture in the pesticide usage survey reports. Surveys are conducted on a rolling programme and not all crops are surveyed each year. These reports are available in the House Libraries.
The song thrush population has declined steeply within the past 25 years, occurring in both woodland and farmland, but that on farmland is substantially greater. The recent breeding bird survey and common bird census trends suggest that the decline has levelled off since the mid-1990s.
Evidence suggests that the decline may have been driven by lower survival rates of birds in their first year and/or by a decline in the number of breeding attempts that pairs are (on average) able to make in each season. This may be related to food availability both in the winter and in the breeding season. Decreasing song thrush abundance has been linked to agricultural intensification, but woodland-specific factors such as drainage and the depletion of the shrub layer may also be implicated.
However, research shows that increasing pesticide use may reduce food availability and indirectly contribute to the decline in 20 species of song birds, including the song thrush. In areas of mixed farmland landscapes, woodland and grassland provide important foraging habitats. In arable landscapes where these habitats are scarce the birds used gardens and arable fields in the breeding season. Thus in landscapes dominated by arable farmland, reductions in invertebrate availability due to pesticide application (as well as other factors of intensification) may affect song thrushes.