English
A study identified two factors that may limit breeding productivity of the Reed Bunting Emberiza schoeniclus, which is in significant decline in England since the 1990s: ground vegetation providing concealment from nest predators and availability of invertebrate prey for chicks. The increased use of pesticides may have reduced invertebrate densities on most farmland.
There has been a massive 95% decline in the UK Tree Sparrow Passer montanus population between 1974 and 1999. The nestling diet of Tree Sparrows is largely composed of invertebrates. It is possible that due to agricultural intensification in the late 20th century and increased use and effectiveness of insecticides there has been a decline in invertebrate prey, rendering large areas of farmland as suboptimal breeding habitat for Tree Sparrows.
Starling Sturnus vulgaris populations have declined throughout Europe over the last two decades. The Starling is commonest in urban and farmland habitats, though density in the latter is much lower. Soil and ground-dwelling invertebrates, particularly leatherjackets (tipulid larvae) and earthworms, are the main prey of Starlings. The use of insecticides on grassland is targeted partly at tipulids, which may have reduced foraging opportunities for Starlings.
There has been a large population decline of the song thrush Turdus philomelos in Britain during the last three decades, which has reduced breeding densities on farmland by nearly 70% between 1968 and 1999. Survival of birds in their first year of life after fledging was shown to have a great impact on population changes. Changes in survival in the first winter are sufficient to have caused the song thrush population decline. Earthworms and other soil-dwelling invertebrates form a large component of the diet of song thrushes, particularly between December and May. Earthworms move deeper into the soil and/or become inactive during periods of cold weather and hence become less available as prey for song thrushes. Reduced availability of invertebrate food could explain reduced survival in the winter.
We compared bird communities of paired extensively and intensively grazed cattle pastures in three different regions of the Hungarian Great Plain. The extensive field and intensive field in a pair had the same soil type and groundwater level and were situated in similarly structured landscapes. Cattle density was about 0.5 cows/ha on extensive and greater than 1 cow/ha on intensive fields. None of the fields were fertilised, cut or re-seeded. We found significant effects of grazing intensity on the abundance of grassland birds, which were more abundant on the extensive sites, whereas no effects were found on non-grassland birds. The three commonest grassland species (Skylark Alauda arvensis, Yellow Wagtail Motacilla flava and Corn Bunting Miliaria calandra) were more abundant on the extensive fields in all regions.
In recent decades, the West European population of Black-tailed Godwits Limosa limosa (located mainly in the Netherlands) has declined at a quite alarming rate (5% per annum primarily due to declining productivity from 0.7 fledged young/pair in the 1980s to 0.2 fledged young/pair now) while the Icelandic population has undergone a rapid increase in population size (with a productivity likely to be 0.5-0.8 chicks/pair). The breeding habitats in the Netherlands, Germany, Belgium and Denmark are intensively farmed grasslands with high ground water levels in open landscapes, while in Iceland the breeding habitats are lowland marshes and dwarf-birch bogs. Godwits preferentially choose areas with high groundwater levels as breeding sites.
John Pickrell in England for National Geographic News
February 2, 2004
Bat activity may be up to 60 percent greater on organic farms than conventional farms in the United Kingdom, according to a new report. The study also revealed that one endangered European bat was completely absent on non-organic farms tested. A second study, published in the science journal Conservation Biology, reveals that insect families which are key to British bat's diets are significantly more abundant and diverse on organic farms.
In the last few decades bat populations have been declining at alarming rates worldwide. Bats remain the most endangered land mammal in the United States. An important factor could be increased use of pesticides, both in agriculture and in the treatment of building materials against pests. Bats are the primary predators of night-flying insects and will live or relocate to areas where there are lots of insects.
BY SONIA SHAH
For decades, toxicologists have accrued a range of evidence showing that low-level pesticide exposure impairs immune function in wildlife, and have correlated this immune damage to outbreaks of disease. In the past dozen years, three new diseases have decimated populations of amphibians, honeybees, and — most recently — bats. Increasingly, scientists suspect that low-level exposure to pesticides could be contributing to this rash of epidemics. The recent spate of widespread die-offs began in amphibians. Scientists discovered the culprit — an aquatic fungus called Batrachochytrium dendrobatidis, of a class of fungi called “chytrids” — in 1998. Its devastation, says amphibian expert Kevin Zippel, is “unlike anything we’ve seen since the extinction of the dinosaurs.” Over 1,800 species of amphibians currently face extinction. There is a strong correlation between pesticide use and declining amphibian populations. Six years after scientists discovered the fungal assault on amphibians, a mysterious plague began decimating honeybees.
Recent large declines in house sparrow Passer domesticus populations in many European towns and cities have generated much speculation as to possible environmental causes. Reproductive failure linked to inadequate invertebrate availability provides a plausible demographic mechanism accounting for declines in urban-suburban house sparrow populations.