Are Toxic Agrichemicals Forcing Rapid Evolution in Yellowstone Elk?
New research suggests hazardous chemicals like pesticides and fertilizers used in farming, more so than wolves, contributed to decline in Greater Yellowstone elk and other ruminants
A recent review paper published in the scientific journal Chemosphere suggests that deformities and reproductive issues in Greater Yellowstone wildlife over two decades may be connected to a surge in the use of hazardous chemicals used in farming that was documented at the same time. Here, an aerial view shows an agricultural crop duster flying low over a potato field, spraying chemicals. Photo by B. Brown/Shutterstock
CORRECTION: The article below incorrectly referred to elk calf research conducted in the Jackson, Wyoming area by biologist Doug Smith. We've corrected the piece to indicate the research was conducted by biologist Bruce L. Smith.
by
Laura Lundquist
In
the spring of 1995, Bob and Judy Hoy began to see disturbing trends in the
animals around their Stevensville home south of Missoula, Montana.
“I
noticed things were dying that shouldn’t be dying,” Judy said in a May 2022
interview. “Baby marmots just disappeared. All of the toads in our yard just
disappeared. Then people in the neighborhood who had livestock, their livestock
were born with very short upper faces, causing them to have underbites.”
The
Hoys both had biology backgrounds—Bob was a game warden with Montana Fish,
Wildlife and Parks and Judy was a biology teacher and wildlife rehabilitator—so
they started piecing events together. Their suspicions increased a year later
when Bob picked up several road-killed whitetail deer and eight out of nine
yearling bucks had malformed reproductive organs. Some deer also had underbites
due to shortened noses, the same as the livestock.
For
the next 20 years, the Hoys tracked similar deformities and reproductive
problems in Montana’s wildlife from the Bitterroot Valley into the Greater
Yellowstone Ecosystem. Bison calves were found with shortened noses and some
bulls had noticeably short scrotums. Elk calves were smaller and developed
slower. The deformities seem to fit a pattern of teratogenesis, where
deformities and deaths are caused by chemicals or viruses that damage an
organism’s development. Thalidomide, for example, is a teratogen that pregnant
women took for nausea in the mid-20th century, but which was later found to
inhibit limb growth in their children.
Even back in the 1990s, Hoy suspected the wildlife deformities were related to the increased use of agrichemicals—chemicals used to eliminate herbivorous insects, fungi and weeds to maximize crop harvests—in the fields of Montana and surrounding states.
Now, Judy
and two other researchers have published a review paper that pieces together
her observations and similar wildlife problems documented in Montana during
that 20-30-year span. They then present recent research suggesting the problems
could be connected to a surge in the use of hazardous chemicals used in farming
that was documented at the same time. Their review paper was published last month in the May issue of the peer-reviewed scientific
journal Chemosphere.
“The paper is
primarily concerning the Greater Yellowstone Ecosystem and effects of
teratogenic toxins on the wildlife there and in surrounding states,
especially Montana and Wyoming,” Judy Hoy wrote in a May 22, 2024 email to Mountain
Journal. “The general public needs to know about the serious effects
that are happening to vertebrates, especially mammals, since humans are
mammals.”
The graphic above from the review paper indicates general regions of intensive agriculture (P indicates major potato-growing areas), and the prevailing southwest wind direction influencing the Greater Yellowstone area (heavy dashed arrow).
Even back
in the 1990s, Hoy suspected the deformities were related to the increased use of agrichemicals—also called agrochemicals—used to eliminate herbivorous insects, fungi and weeds to maximize crop
harvests in the fields of Montana and surrounding states. Her suspicions were reinforced when she learned that a
1991-1992 University of Montana study of whitetail deer on the Lee Metcalf National Wildlife Refuge near Stevensville found no defects.
The
Hoys reported their findings to Montana Fish, Wildlife and Parks in the
mid-‘90s, but Judy says they weren’t taken seriously. In 1999, however, the
U.S. Fish and Wildlife Service at the Lee Metcalf Refuge created a six-member
study group of
veterinarians and biologists to determine whether
pesticides were responsible for the wildlife anomalies.
While
verifying that Hoy’s wildlife observations were real, the group report said
they were unable to make any pesticide connection. The study group
was “distressed” to learn they couldn’t find
any information on pesticide application in Ravalli County due to the minimal
data the state gathered at the time. Congress
An elk calf with a severe underbite; the premaxillary bone is underdeveloped, thus short and narrow. Photo courtesy Chemosphere
had passed the Food Quality
Protection Act only a few years earlier mandating pesticides be assessed for
their ability to disrupt the endocrine or hormone system. The screening and
testing methods for endocrine disruption are still being developed.
“While
the implication of pesticide exposures and disruption in calcium-signaling are
intriguing, we simply could not find enough hard evidence to confirm this
conclusion,” the group concluded, adding that further investigation was
justified.
The
U.S. Fish and Wildlife Service didn’t follow up. But in the 25 years since the
report, other researchers have. Hoy and two other researchers cite dozens of those studies in their review
to build a picture of how a documented surge in the use of agrichemicals in the
1990s could have affected elk, deer and other ruminants in southwestern Montana
and Yellowstone National Park to the point that it contributed to population
declines.
Some
have blamed the decline of elk populations in Yellowstone, particularly the
Northern Herd, on wolves, which were reintroduced in 1995-96. After all, the review
paper cites, “between 1994 and 1997–98, the
winter counts of the population of northern
Yellowstone elk declined by
This mule-deer fawn displays a severe underbite, crooked teeth, and incisors much wider than its underdeveloped dental pad. Photo courtesy Chemosphere
one third [and] the 2013 winter counts indicated
declines of more than 75 percent over two decades.”
But
the paper points out that new wolf packs living in the park could not have
eaten enough to account for the population loss of about 10,000 elk between
1994 and 2004. The average of 130 wolves that tend to inhabit the park would
have each had to eat 20-22 elk annually, which is highly unlikely since they
also eat other animals. A range of carnivores eat elk, but the review found that “most
scientific investigations concluded that unknown or unexplained factors were
likely involved.”
The
review cites elk research that former Yellowstone biologist and wildlife manager Bruce L. Smith carried
out near Jackson Hole, Wyoming. Elk calves captured in 1990, 1991 and 1992 were
healthy enough to join the herd after about 12 days and none were killed by
predators after that. However, when the same research was
carried out in 1997, 1998 and 1999, the calves, especially females, were
smaller and grew slower, so they suffered four times more predation than calves
from the early study. Other studies in the park found cow-calf ratios of 30-40
calves per 100 cows dropped after 1994 to less than 20 calves per 100 cows. Aside
from predation, the causes of death in the later calves included heart defects
or difficult births.
What
caused elk calves born in the late 1990s to fail to thrive compared with those
in the earlier study? Similarly, what caused whitetail deer in the Bitterroot
Valley to develop deformities after 1995 and prompted a rise in reports around
the same time of domestic animals born with malformations and health issues?
Hoy and her colleagues note that "the second study period occurred following
the massive increases in regional use of teratogenic agrichemicals.”
The
review details how the use of three kinds of agrichemicals—now recognized as
teratogens—surged in the crop fields of Washington, Oregon, Idaho, Montana and
the Dakotas between 1994 and 1996 and describes how the animals who browse or
live in vegetation sprayed or indirectly contaminated by such chemicals could
have been harmed.
"We grew up on a dairy farm and put malathion on our cows before we milked them. It’s equivalent to the smoking issue in that there’s too much economic interest in the use of these chemicals.” – Pamela Hallock Muller, scientist, coauthor, Teratogenic Agrichemicals, Chemosphere
In
1994, a regional outbreak of blight led to a 10-fold increase in the use of
chlorothalonil fungicides in the potato fields of Washington, Oregon and Idaho.
Unintended spray drift and deposition of chlorothalonil in rain and snow has
been shown to contaminate plants and surface waters across extensive areas.
Such fungicides contain cyanide and are most toxic when inhaled. Studies show
laboratory animals exposed to chlorothalonil suffered embryo loss, kidney and
liver damage and chromosome aberration.
“Damage
to the liver and kidneys can interfere with an exposed animal’s ability to
detoxify and excrete other toxins to which it is exposed,” according to the
review. “Thus, synergy with other pesticides in the environment likely results
in greater injury to the internal organs.”
There
were plenty of other pesticides. Also in 1994, people started spraying a newly
registered neonicotinoid insecticide called imidacloprid in Oregon, Washington and
Idaho. Plants take up the synthetic nicotine, which damages the nervous systems
of insects that eat the plants. However, neonicotinoid insecticides are also
implicated in the decline of several species that pollinate flowers, such as
the western bumble bee.
The paper points out that new wolf packs living in the Yellowstone National Park could not have eaten enough elk to account for the population loss of about 10,000 elk between 1994 and 2004.
But
in vertebrates, imidacloprid is an endocrine disruptor, acting on the hormone
system. In 2015, a South Dakota State University researcher gave varying
amounts of imidacloprid to captive whitetail does and found the does that
received the chemical had offspring with underbites and malformed reproductive
organs. And the higher the amount of imidacloprid, the worse the deformities
and fawn survival.
Finally,
in 1996, the introduction of Roundup Ready crops—those that are resistant to the Monsanto-produced
herbicide Roundup—resulted in farmers using even greater amounts of
glyphosate-based herbicides or GBH. GBH reduces plant uptake of essential
minerals such as manganese, which means herbivores can suffer mineral
deficiencies that impair their metabolism. In addition, studies have found that
direct exposure to GBH can cause major reproductive problems, including
preventing pregnancy or producing offspring that are stillborn or have
abnormalities. Another study cited in the review found problems associated
with GBH exposure can be expressed in offspring two or three generations later.
The
review claims that GBH exposure alone could explain the decline in the
Yellowstone elk populations and the low cow-calf ratios Smith found in the
Jackson area. But the combination of all three agrichemicals that surrounded
southwest Montana could have interacted in varying amounts to worsen the
effects on animals. Studies have shown that organisms downwind of treated
fields can be exposed to toxic mixtures of pesticides.
However,
even though the use of agrichemicals hasn’t diminished, the review authors
noted that the Yellowstone elk population started to recover after 2014,
although cow-calf ratios are still low. They’ve also seen far fewer ruminants
with birth defects since 2014, but they’ve observed that the sex ratio has
skewed more toward females. They suggest that
this could be the result of rapid natural selection in response to the agrichemicals.
Females more susceptible to the chemicals died or failed to reproduce while more resistant females prospered. In short, if agrichemicals did play a
role, Yellowstone elk and other ruminants could have adapted over a few
generations to better withstand the worst effects of the substances.
The
need to investigate the dangers of toxic agrichemicals, however, remains. The
authors write that “even if selection occurs in wildlife for genotypes most
resistant to endocrine disruption, the effects of ubiquitous teratogens on the
health of domestic ruminants and other animals, including humans, will likely
continue and possibly accelerate.”
A low-flying crop duster sprays green farmland in Idaho Falls, Idaho on August 16, 2012. Photo by B. Brown/Shutterstock
Coauthor
Pamela Hallock Muller, University of Southern Florida oceanographer and Hoy’s
sister, said some of the research they cited has only recently been published
because scientists have been sometimes discouraged from delving into the
hazards of agrichemicals. And money
for such research isn’t provided. So, people who
suspect that harm is occurring have a hard time getting the public to pay
attention to potential problems.
“The
endocrine disruptors are something I’ve been interested in, partly because I’m
female and I was born at a time when people used DDT,” Muller said in a recent interview with Mountain Journal. “My mother
thought insects were bad and DDT was good. We grew up on a dairy farm and put
malathion on our cows before we milked them. It’s equivalent to the smoking issue in that there’s too much
economic interest in the use of these chemicals.”
DDT
was banned in 1972 due to its persistent toxicity and its effects on human and
animal reproduction. The insecticide malathion,
which attacks insects’ nervous systems like neonicotinoids, is still being used
although environmental advocates, including the Center for Biological
Diversity, have repeatedly sued the Environmental Protection Agency for two
decades to get it to consult with the Fish and Wildlife Service about the
effects on wildlife. The history of the lawsuits backs up Muller’s description
of the difficulties in documenting and regulating industrial chemicals.
“The general public needs to know about the serious effects that are happening to vertebrates, especially mammals, since humans are mammals.” – Judy Hoy, researcher, coauthor, Teratogenic Agrichemicals, Chemosphere
In January
2017, the EPA determined in a biological evaluation that 97 percent of
federally protected species are likely harmed by malathion. But under the Trump
administration and at the request of the manufacturer Dow Chemicals, the EPA
and Fish and Wildlife Service indefinitely suspended the malathion assessment.
The Center
for Biological Diversity sued again but the Biden
administration agreed to resume the assessment. A 2021 U.S. Fish and Wildlife Service draft biological
opinion determined that malathion jeopardized
78 listed species. But the following year, the
agency walked back its draft finding
after chemical manufacturers pledged to change product labels to better inform consumers. This April, the EPA issued guidance
on the labels.
The Center
for Biological Diversity has the financial resources to force agencies to
investigate chemical hazards. Hoy and her coauthors don’t. They’ve tried to
gather the data and draw the connections themselves. But since Hoy is in her
80s, this review is likely her swan song.
“I’m
making one last gasp trying to get these critters saved before it’s too late,”
Hoy said. “Neonicotinoids and glyphosate work together, causing everything to
die 1,000 times faster.”
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About Laura Lundquist
Laura Lundquist earned a journalism degree from the University of Montana in 2010, and has since covered the environmental beat for newspapers in Twin Falls, Idaho and Bozeman, in addition to a year of court reporting in Hamilton. She's now a freelance environmental reporter with the Missoula Current Online Journal.
