Impacts of Pesticides on Birds

Birds can be exposed to pesticides directly through ingestion of seeds that have been treated with pesticides, or indirectly through consumption of small insects and other animals that have ingested the pesticides themselves, leading to secondary poisonings of the bird. They can also be indirectly affected through decline in insect population. When the insect population is reduced, this natural food source for birds is also reduced.  


Bioaccumulation refers to the phenomenon where chemicals or toxic substances build up in an organism’s body. This can occur when these chemicals accumulate faster than the body can metabolize them.

A number of terms fall under the bioaccumulation definition. Each of these terms are important for understanding the big picture – how chemicals can affect us all, even if it only seems they are affecting a small portion of the world.

Bioconcentration is a specific process within bioaccumulation which describes when the concentration of chemicals in an organisms body becomes higher than the concentration of chemicals in the environment surrounding the organism. An example of this could be a river or lake that has low levels of a chemical in the water.  Over time, aquatic organisms that live in the contaminated waters would absorb those chemicals through their gills or skin. Because they are consistently exposed to low levels, their bodies cannot metabolize the chemicals quick enough, causing them to accumulate within the organism. Eventually, the contaminants will build up to a point where there is a higher concentration in the organism than in the waters around them.

Biomagnification is a specific process within bioaccumulation where the accumulation of a chemical grows larger as it moves up the food chain. An example of this could be that a shrimp gets consumed by a fish which is consumed by a bigger fish which is then consumed by a human. The bioaccumulation of a chemical is much lower in the shrimp, and has magnified exponentially through the food chain to be much higher in the big fish, and even higher in the human. 

  • In 2015, a study published in Chemosphere found that low dose pesticide exposure to imidacloprid, a commonly used neonicotinoid, and mancozeb, a fungicide, can cause alterations in the thyroid gland of a bird, impacting thyroid homeostasis and reproduction.
  • In 2014, a forensic study of bird carcasses that had been exposed to DDT, a toxic and persistent organophosphate, revealed liver and brain abnormalities, even though DDT has been banned since 1972. Exposure to DDT and subsequent bioaccumulation can also impact normal functioning.  
  • A 2013 study published by Pierre Mineau, PhD, pointed to pesticide use as the single most important indicator of grassland bird declines in the U.S.  Researchers found that the best predictors of bird declines were lethal pesticide risk, insecticide use and loss of cropped pasture.
  • In 2014, Dutch scientists established an indirect link between neonicotinoid use and insect-eating birds. The report provides evidence that neonicotinoids are indirectly hurting larger creatures by reducing insect prey populations such as mosquitoes and beetles.
  • Another study by Pierre Mineau, PhD, linked neonicotinoids to acute and chronic bird deaths. The report states that “a single corn kernel coated with a neonicotinoid can kill a songbird. Even a tiny grain of wheat or canola treated with the oldest neonicotinoid, imidacloprid, can poison a bird. As little as 1/10th of a corn seed per day during egg-laying season is all that is needed to affect reproduction with any of the neonicotinoids registered to date.”
      • This report concluded that neonicotinoids are toxic to birds and to the aquatic systems on which they depend, prompting calls for a ban on their use as seed treatments and a suspension of all applications from various environmental organizations.

The full impact of pesticide exposure to bird diversity is difficult to ascertain due to the elusive nature of most birds. They may be exposed and then migrate, dying far from the treated area. Their carcasses also disappear quickly, eaten or moved by scavengers within a day or so. A 2005 study by David Pimentel, PhD, stated that it is assumed that approximately 72 million birds are killed due to some form of pesticide exposure each year.             

Economic Cost

According to a 2011 National Survey of Fishing, Hunting and Wildlife-Associated Recreation, published by the Fish and Wildlife Service (FWS), about 47 million Americans observed birds in 2010. Wildlife refuge visitation is a large part of birding activity, which brings in considerable revenue.  According to FWS, “the monetary value of economic activity generated by birding visits to refuges totaled $257 million in 2011. In turn, this generated $73.9 million in job income and 3,269 jobs.” In an addendum to the 2011 National Survey of Fishing, Hunting, and Wildlife-Associated Recreation, the FWS estimated that “trip-related and equipment-related expenditures associated with birding generated nearly $107 billion in total industry output, 666,000 jobs, and $13 billion in local, state, and federal tax revenue.”

Birds also provide a multitude of ecosystem services, which are any positive benefit that wildlife provides to people. The benefits can be direct or indirect – small or large. These services can range from dispersing seeds to acting as natural pest predators and as indicators of environmental and human health. As a result of bird declines due to pesticide exposure, it can be assumed that the cost of birding activities will increase due to low supply and high demand, jobs and revenue will dwindle, and important and necessary ecosystem processes will be lost.

Litigation & Lawsuits 

by USFWSmidwest
 Whooping Cranes. Photo by USFWSmidwest.

In 2015, EPA was sued for violating the Endangered Species Act (ESA). The lawsuit documents EPA’s failure to consult with the U.S. Fish and Wildlife Service (FWS) regarding the impact of the Enlist Duo, an herbicide consisting of glyphosate and 2,4-D that is intended to be sprayed on crops resistant to those chemicals, on two endangered species: the whooping crane (and also the Indiana bat). A motion was filed against EPA after the decision was made to expand the use of Enlist Duo to nine additional states.


Quick Links

In July 2014, FWS decided that it will begin to phase out the use of GE crops to feed wildlife and ban neonicotinoid insecticides from all wildlife refuges nationwide by January 2016. This new policy still allows for case-by-case exceptions. GE crops and neonicotinoid pesticides often interfere with the protection of wildlife that US national refuge systems are designed to protect, but despite this, these harmful practices were often used. Scientists warn that the use of GE crops can lead to increased pesticide use on refuges through pesticide resistance, where weeds become resistant, therefore a greater amount of pesticides must be used. This overuse negatively affects birds and other wildlife. In March 2015, a federal court ruled against the use of neonicotinoid insecticides in national wildlife refuges in the Midwest region.  The ruling capped a legal campaign by Beyond Pesticides and other environmental organizations to end the planting of GE crops and other industrial agricultural practices on national wildlife refuges.             

Quick Links

What Can You Do?