Pesticides, Continued: A Decline in Grassland Birds Is Linked to Agricultural Pesticides

American Kestrel numbers are falling, perhaps because of pesticides. Connecticut Audubon Society photo by Scott Kruitbosch.

Aerial insectivores aren’t the only category of common birds that are becoming far less common.

As we noted in our Connecticut State of the Birds 2013 report, populations of aerial insectivores such as Barn Swallows, Chimney Swifts, Common Nighthawks, and various flycatchers – birds that eat only insects they catch on the wing – have dropped dramatically since at least the 1960s.

But grassland birds are declining too. A year ago, in Sanctuary, the journal of the Massachusetts Audubon Society, ornithologist and writer Chris Leahy noted that it is no longer easy to find American Kestrels and Eastern Meadowlarks in New England:

“All but taken for granted as common roadside birds as late as the 1980s, the kestrel and meadowlark have plummeted alarmingly within just a few decades throughout much of their range. Initially an obvious cause presented itself. These are birds of agricultural habitats, and everyone knows that farmland in New England is fast becoming part of a historical landscape; surely these birds were classic victims of habitat loss. But birdwatchers who pay close attention to their local patches of habitat noted that kestrels and meadowlarks are now absent from places where they were recently common – even though the critical elements of their habitat were still amply present.”

The title of Leahy’s piece was, “Of Kestrels, Meadowlarks, and Polybrominated Diphenyl Ethers,” and he went on to note that almost three-quarters of what kestrels and meadowlarks eat are bugs – and then to argue that we’re seeing fewer of those field birds because pesticides use is pervasive.

Then late last month, just as we were releasing this year’s Connecticut State of the Birds, the online journal PLOS ONE published a peer-reviewed study called, “Pesticide Acute Toxicity Is a Better Correlate of U.S. Grassland Bird Declines than Agricultural Intensification.”

What that title means is this: the decline of grassland birds is more closely linked to pesticide poisoning than to habitat change. The birds include Grasshopper Sparrow, Vesper Sparrow, Savannah Sparrow, Northern Harrier, Bobolink and Eastern Meadowlark.

The authors, Pierre Mineau and Mélanie Whiteside, write:

“Our results suggest that the use of lethally toxic insecticides cannot be ignored when trying to identify causes of grassland population declines in North America. Indeed, they offer a more plausible explanation for overall declines than does the oft-cited ‘habitat loss through agricultural intensification’. “

Among other points, they say that even when only a small proportion of total cropland is treated, it affects overall bird population trends. And although pastures are believed to be safer for birds than cropland, a common pasture crop, alfalfa, carries the third highest lethal risk of any crop based on pesticide use.

The stakes are high. The authors note that 215 species of neotropical migrants use agricultural areas in North America. And the exposure and mortality are significant:

Bobolinks are among the grassland birds that are in decline. Connecticut Audubon Society photo by Scott Kruitbosch.

“ … 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 direction. The Avian Incident Monitoring System (AIMS), a joint project of the U.S. Environmental Protection Agency (EPA) and the American Bird Conservancy (ABC), listed 113 pesticides which have caused direct bird mortality. An analysis of a large number of avian field studies suggests that avian kills were a normal corollary of insecticide use in many crops grown in North America. For example, analyses of granular insecticide use patterns in western Canada indicated that the abundance of several common species was negatively correlated with these toxic insecticides.”

One commonly-cited study “estimated that pesticide-induced direct mortality numbered approximately 67 million per year in the U.S. … This estimate was undoubtedly quite conservative.”

And in another study, Pierre Mineau, one of the authors of the PLOS ONE paper, “estimated, based on several industry-led field studies that at its peak, a single use pattern (for corn rootworm) of a single insecticide (carbofuran), in a single crop (corn) was killing 17 to 91 million songbirds annually in the U.S. Midwest.”

You have to look hard for good news in this, but Mineau and Whiteside offer some:

“An analysis of pesticide use patterns in the US does suggest that the situation is improving as a result of the gradual withdrawal of the most toxic products, largely because of human health concerns. The current analysis considered bird trends from 1980 to 2003; there is evidence that the acute lethal risk to birds was already dropping during the second half of that period.”

There are several pesticide bills being considered by the Connecticut General Assembly in Hartford this year – bills that would ban the use of lawn pesticides in parks and schools, and ban the use of two particular pesticides in the coastal area. Connecticut Audubon Society supports them all. Details and links are on our Legislative Tracking page. — Tom Andersen, director of communications and community outreach