Bird populations in many regions of the U.K. have declined dramatically in the last 25 years, according to a report by the Royal Society for the Protection of Birds (RSPB). The report links pesticide use with declining populations in a number of bird species. It says that elimination of food sources -- not direct poisoning -- is the main threat to birds from pesticides. Other reasons for the decline may be related to changes in agricultural practices, such as making silage instead of hay, thereby removing food and cover for bird and insect populations earlier in the season. Winter cropping, in which farmers use pre-emergent herbicides to "clean" fields, may also be a factor by reducing over- wintering habitat for birds.

According to the report, pesticides can reduce birds' food sources in three ways:
-- Insecticides may reduce the abundance of invertebrates, an important food source during the breeding season.
-- Herbicides may reduce the number of host plants, reducing the numbers of invertebrates that depend on them.
-- Herbicides may also reduce the abundance of weeds and seeds which provide food for birds in winter and for some species during breeding.

Bird species that show a serious decline in populations between 1969 and 1994 include: tree sparrow (89% decline), gray partridge (82%), turtle dove (77%), bullfinch (76%), song thrush (73%), lapwing (62%), reed bunting (61%), skylark (58%), linnet (52%), swallow (43%), blackbird (42%), and starling (23%).

The RSPB report showed that butterflies, moths, beetles and grasshoppers were more prominent in the diets of bird species that were declining, while species that were stable or increasing had diets consisting primarily of woodland type plants.

Pesticide use in the U.K. has been steadily increasing since the early 1970s. Ministry of Agriculture figures show that cereal crops are now sprayed with six times as many fungicides as in the 1970s and twice as many herbicides. Frequency of pesticide applications on cereal crops has nearly tripled in the past 25 years.

The report makes several recommendations for changes in agricultural practices, including that farmers be encouraged to switch to organic practices and that regulators set targets for reducing pesticide use. It also called for better monitoring of pesticide impacts on invertebrates and plants, more research on the ecology of individual bird species and large scale experimental studies assessing the effects of pesticides and other agricultural factors on wildlife.

The Pesticides Trust (a UK-based non-governmental organization) commented on the report by calling for a drastic reduction in pesticide use to slow the decline in bird populations. The organization stated that it is now time to consider a tax on pesticide use in the UK and severe restrictions on targeted products that may most affect biodiversity -- such as broad spectrum organophosphate insecticides.

"The Indirect Effect of Pesticides on Farmland Birds" was prepared by BirdLife International, Butterfly Conservation, the Institute of Terrestrial Ecology, Oxford University, Plant life and the RSPB on behalf of the Department of the Environment, Joint Nature Conservation Committee and English Nature. Available from Natural History Book Service Ltd, 2-3 Willis Road, Totnes, Devon, TQ9 5XN, UK. UK$10 (ten pounds) plus UK$2.50 shipping and handling.

Sources: Living Earth: The Magazine of the Soil Association, July 1997. The Pesticide News, June 1997.

Contact: Royal Society for the Protection of Birds, The Lodge, Sandy, Beds, SG19 2DL UK; phone (44-176) 680 551. The Pesticides Trust, Eurolink Centre, 49 Effra Road, London, SW2 1BZ, UK; phone (44-171) 274 8895; fax (44-171) 274 9084; pesttrust@gn.apc.org.