Birds fed a common pesticide lost weight rapidly and had migration delays

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The world’s most widely
used insecticides may delay the migrations of songbirds and hurt their chances
of mating. 

In
the first experiment to track the effects of a neonicotinoid on birds in the
wild, scientists captured 24 white-crowned sparrows as they migrated north from
Mexico and the southern United States to Canada and Alaska. The team fed half of
those birds with a low dose of the commonly used agricultural insecticide imidacloprid
and the other half with a slightly higher dose. An additional 12 birds were
captured and dosed with sunflower oil, but no pesticide.  

Within
hours, the dosed birds began to lose weight and ate less food, researchers
report in the Sept. 13 Science. Birds given the higher amount of
imidacloprid (3.9 milligrams per kilogram of body mass) lost 6 percent of their
body mass within six hours. That’s about 1.6 grams for an average bird
weighing 27 grams. Tracking the birds (Zonotrichia leucophrys) revealed
that the pesticide-treated sparrows also lagged behind the others when continuing
their migration to their summer mating grounds.

The
findings suggest that neonicotinoid insecticides, already implicated in dropping
bee populations, could also have a
hand in the decline of songbird populations across
North America. From 1966 to 2013, the populations of nearly three-quarters of farmland bird species across
the continent have precipitously dropped.

The researchers dosed
the birds in the lab with carefully measured amounts of pesticide mixed with
sunflower oil. In the wild, birds might feed on seeds coated with imidacloprid. The highest
dose that “we gave each bird is
the equivalent of if they ate one-tenth of [a single] pesticide-coated corn
seed,” says Christy Morrissey, a biologist at the University of Saskatchewan in
Saskatoon, Canada. “Frankly, these were minuscule doses we gave the birds.”

seeds
Farmers use seeds coated with neonicotinoids to protect their crops from harmful insects. But the pesticides could harm birds who inadvertently eat treated seeds, researchers say.M. Eng

After observing the
birds in the lab, Morrissey and colleagues tagged the fliers with lightweight
trackers and kept tabs as the sparrows continued their spring migration. The
highest-dosed birds stayed a median of 3.5 days longer near the site where they
were captured — possibly to recover and regain strength — than birds that weren’t
dosed with the pesticide. Birds given the lower dose of pesticide (1.2
milligrams per kilogram of body mass) stuck around for a median of three days,
and those that weren’t dosed with pesticides flew away after half a day.

Even a slight delay
could affect a sparrow’s chances of finding a mate and nesting, Morrissey says. 

In a previous study that observed neonicotinoid-dosed
white-crowned sparrows
in
captivity, the same team found that the pesticide caused the birds to lose
up to a quarter of their body mass and become disoriented (SN: 11/22/17).  

“Given that we’ve been
seeing increasing evidence that these pesticides harm pollinators and insects,
I can’t say I’m shocked or surprised that they also have an effect on birds,”
says Melissa Perry, an environmental and occupational health scientist at
George Washington University in Washington, D.C., who wasn’t involved with the
study.

Much of the research on neonicotinoids, which have chemical
similarities to nicotine, has focused on their effect on beneficial insects, such as bees which play a key role in
plant pollination (SN: 7/26/16). Scientists
are just beginning to evaluate the pesticides’ impact on vertebrates, Perry
says. 

“When
this type of pesticide was first introduced, they were offered as an
alternative to insecticides that were more toxic,” Perry says. “I don’t think
we ever really anticipated the environmental impact of neonicotinoids.”

Outdoor use of
imidacloprid and two other neonicotinoid pesticides is banned in the European Union, but the pesticides are still widely used in the United States (SN: 6/10/19).

Unlike
DDT — an older type of insecticide developed in the 1940s and now banned in the
United States that can accumulate in the environment and persist for decades —
neonicotinoids are quicker to break down, says study coauthor Margaret Eng, a
toxicologist also at the University of Saskatchewan. 

It does seem that after resting for a few days, the birds dosed with the pesticide were able to resume their migration, Eng says. “But there’s still a lot we don’t know about how repeated exposures to the pesticides might affect a bird.”

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