English

There is continuing debate about the impact of agricultural practices on farmland wildlife. In particular, it has been postulated that a general decline in insect abundance linked with intensification of agriculture may have contributed to farmland bird decline. While some autecological studies have supported this hypothesis, larger-scale and long-term studies are needed.

• Suction traps mounted on 12·2-m towers (Rothamsted-type) have been sampling aerial insects for nearly 40 years throughout the UK. Their catches are correlated over large spatial scales. We analysed insect catch data from a single suction trap run for 27 years in a rural location in Scotland, and showed that insect numbers have changed significantly over time, although non-linearly. The multivariate data set (numbers from the 12 common arthropod groups) was summarized using principal components analysis (PCA) to extract three components explaining 62% of the variation.

• We also used PCA to describe agricultural change, using published agricultural data for eight measures of farming in Scotland. Arthropod abundance and principal component (PC) scores were significantly related to the agricultural PC scores as well to summary climatic measures.

• Using Scottish data from the British Trust for Ornithology Common Birds Census, we extracted three PC to describe the time-dependent average densities of 15 common farmland birds in Scotland. Measures of bird density were significantly related to insect abundance and PC scores and, independently, to measures of agriculture and climate.

• These data from a broad suite of species provide support for linked temporal change between farmland birds, invertebrate numbers and agricultural practice in Scotland. Although entirely correlative, the results are consistent with the view that agricultural change has influenced birds through changes in food quality or quantity. The work also shows how large-scale invertebrate sampling, in this case using suction traps, is useful for monitoring farmland biodiversity.

A fundamental problem in estimating biodiversity loss is that very little quantitative data are available for insects, which comprise more than two-thirds of terrestrial species. We present national population trends for a species-rich and ecologically diverse insect group: widespread and common macro-moths in Britain. Two-thirds of the 337 species studied have declined over the 35 yr study and 21% (71) of the species declined >30% 10 yr−1.

Nearly 40,000 conservation-minded drivers counted the bugs splattered on their vehicle number plates this summer, the Royal Society for the Protection of Birds (RSPB) announced yesterday. The motorists were helping the world's first mass survey into possible insect decline, a UK-wide Big Bug Count held throughout June, and the initial results appear to confirm suspicions that insect numbers have fallen, the RSPB said.

For the first time, long-term changes in total aerial insect biomass have been estimated for a wide area of Southern Britain. From 1973 to 2002, there was a significant decline in total biomass at Hereford. The Hereford samples were dominated by large Diptera, particularly Dilophus febrilis, which showed a significant decline in abundance. Diptera have been identified as important in the diets of adult and chicks across a range of species. The declines shown in Hereford are thus likely to have had some effect on the bird populations of the surrounding area.

Monitoring data reveal significant changes in the number of meadow birds in the Netherlands. The overall yearly decline has nearly quadrupled in recent years, i.e. from 1.2% in 1990-2000 to 4.6% since 2000. All meadow birds in the monitoring scheme (Skylark Alauda arvensis, Northern Shoveler Anas clypeata, Yellow Wagtail Motacilla flava, Oystercatcher Haematopus ostralegus, Black-tailed Godwit Limosa limosa, Northern Lapwing Vanellus vanellus, Common Redshank Tringa totanus, Meadow Pipit Anthus pratensis en Tufted Duck Aythya fuligula) are declining since 2000. Songbirds like Skylark, Meadow Pipit and Yellow Wagtail declined up to 30% from year to year in some regions which may lead to a population drop of 75% in only five years. Particularly alarming is the steep decline of meadow birds in the western peat land of the Netherlands (with an overall annual decline of 13% since 2000). The bird decline observed since the nineties correlates well with the increasing use of imidacloprid, which was first introduced in agriculture in 1994 and is now by far the most widely used insecticide. Imidacloprid is may leach from soil and is a major surface water pollutant in the Netherlands, particularly in the western part of the country.