A new study in North America has identified acutely toxic pesticides as the most likely leading cause of the widespread decline in grassland bird numbers in the United States, a finding that challenges the widely-held assumption that loss of habitat is the primary cause of those population declines. Download the study for free here
Although this study focusses on the situation in North America it does state that: Common agricultural birds are in decline, both in Europe and in North America. Evidence from Europe suggests that agricultural intensification and, for some species, the indirect effects of pesticides mediated through a loss of insect food resource is in part responsible (for declines).
The scientific assessment, which looked at data over a 23-year period (1980 to 2003) has just been published. The study looked at five potential causes of grassland bird declines besides lethal pesticide risk: change in cropped pasture such as hay or alfalfa production, farming intensity or the proportion of agricultural land that is actively cropped, herbicide use, overall insecticide use, and change in permanent pasture and rangeland.
“What this study suggests is that we need to start paying a lot more attention to the use of pesticides if we want to reverse, halt or simply slow the very significant downward trend in grassland bird populations. Our study put the spotlight on acutely toxic insecticides used in our cropland starting after the Second World War and persisting to this day – albeit at a lower level. The data suggest that loss of birds in agricultural fields is more than an unfortunate consequence of pest control; it may drive bird populations to local extinction,” co-author Pierre Mineau said.
Many grassland bird species have undergone range contractions or population declines in recent decades. In fact, analyses of North American birds indicate that these birds are declining faster than birds from other biomes (a situation mirrored in Europe). Habitat protection has long been considered a central pillar in efforts to stem the decline of grassland bird species.
“We are still concerned about loss of habitat in agriculture, range management, and urban development,” said Cynthia Palmer, manager of the Pesticides Programme at American Bird Conservancy. “This study by no means diminishes the importance of habitat fragmentation and degradation. But it suggests that we also need to rein in the use of lethal pesticides in agriculture, and that we need to be especially careful about any new pesticides we introduce into these ecosystems such as the neonicotinoid insecticides. It reminds us that the poisonings of birds and other wildlife chronicled a half century ago by famed biologist and author Rachel Carson are by no means a thing of the past.”
The study found that lethal pesticides were nearly four times more likely to be associated with population declines than the next most likely contributor, changes in cropped pasture – an important component of habitat loss associated with agricultural lands. The publication says that “…..large quantities of products of very high toxicity to birds have been used for decades despite evidence that poisonings were frequent even when products were applied according to label directions.”
The authors argue that only a small proportion of total cropland needs to be treated with a dangerous pesticide to affect overall bird population trends. Pesticide drift from croplands is also affecting birds that favour the adjoining grasslands.
The study found that declines of grassland birds were much more likely in states with high use of toxic insecticides lethal to birds. The current study relies on pesticide data from the 1980s and early 1990s, a time when organophosphates such as Diazinon and Chlorpyrifos, and carbamates such as Carbofuran and Methomyl, were still largely in vogue. Since that time, a new class of insecticides, the neonicotinoids, have soared to the top of global pesticide markets. Unfortunately, a major toxicological assessment soon to be released by American Bird Conservancy puts to rest any notion that birds and other organisms will fare much better under the new pesticide regime. Neonicotinoids have also been implicated in declines of bees – see the latest RSPB statement on use of these pesticides here