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.    

[See More Scientific Studies]

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.


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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.             

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Scientific Studies: 

  • Assessing Marine Endocrine-Disrupting Chemicals in the Critically Endangered California Condor: Implications for Reintroduction to Coastal Environments.
    Coastal reintroduction sites for California condors (Gymnogyps californianus) can lead to elevated halogenated organic compound (HOC) exposure and potential health impacts due to the consumption of scavenged marine mammals. Using nontargeted analysis based on comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC×GC/TOF-MS), we compared HOC profiles of plasma from inland and coastal scavenging California condors from the state of California (CA), and marine mammal blubber from CA and the Gulf of California off Baja California (BC), Mexico. We detected more HOCs in coastal condors (32 ± 5, mean number of HOCs ± SD, n = 7) than in inland condors (8 ± 1, n = 10) and in CA marine mammals (136 ± 87, n = 25) than in BC marine mammals (55 ± 46, n = 8). ∑DDT-related compounds, ∑PCBs, and total tris(chlorophenyl)methane (∑TCPM) were, respectively, ∼7, ∼3.5, and ∼148 times more abundant in CA than in BC marine mammals. The endocrine-disrupting potential of selected polychlorinated biphenyls (PCB) congeners, TCPM, and TCPMOH was determined by in vitro California condor estrogen receptor (ER) activation. The higher levels of HOCs in coastal condors compared to those in inland condors and lower levels of HOC contamination in Baja California marine mammals compared to those from the state of California are factors to consider in condor reintroduction efforts.
    [Stack, Margaret E., Jennifer M. Cossaboon, Christopher W. Tubbs, L. Ignacio Vilchis, Rachel G. Felton, Jade L. Johnson, Kerri Danil, Gisela Heckel, Eunha Hoh, and Nathan G. Dodder. Environmental Science & Technology.]
  • Deterrence of birds with an artificial predator, the RobotFalcon
    Collisions between birds and airplanes can damage aircrafts, resulting in delays and cancellation of flights, costing the international civil aviation industry more than 1.4 billion US dollars annually. Driving away birds is therefore crucial, but the effectiveness of current deterrence methods is limited. Live avian predators can be an effective deterrent, because potential prey will not habituate to them, but live predators cannot be controlled entirely. Thus, there is an urgent need for new deterrence methods. We developed the RobotFalcon, a device modelled after the peregrine falcon, and tested its effectiveness to deter flocks of corvids, gulls, starlings and lapwings. We compared its effectiveness with that of a drone, and of conventional methods routinely applied at a military airbase. The RobotFalcon scared away bird flocks from fields immediately, and these fields subsequently remained free of bird flocks for hours. The RobotFalcon outperformed the drone and the best conventional method at the airbase (distress calls). Importantly, there was no evidence that bird flocks habituated to the RobotFalcon over the course of the fieldwork. We conclude that the RobotFalcon is a practical and ethical solution to drive away bird flocks with all advantages of live predators but without their limitations.
    [Storms, R.F., Carere, C., Musters, R., van Gasteren, H., Verhulst, S. and Hemelrijk, C.K., 2022. Journal of the Royal Society Interface, 19(195), p.20220497.]
  • Feeding on grains containing pesticide residues is detrimental to offspring development through parental effects in grey partridge.
    Numerous toxicological studies have shown that ingestion of pesticides can induce physiological stress in breeding birds, with adverse consequences on egg laying parameters and offspring quality through parental effects. However, previous studies do not mimic current levels of pesticide residues in typical landscapes, and they do not consider potential cocktail effects of pesticides as they occur in the wild. Herein, we explored whether realistic pesticide exposure affected reproduction parameters and offspring condition through parental effects in Grey partridge. We fed 24 breeding pairs with either seeds from conventional agriculture crops treated with various pesticides during cropping, or organic grains without pesticide residues as controls. The conventional and organic grain diets mimicked food options potentially encountered by wild birds in the field. The results showed that ingesting low pesticide doses over a long period had consequences on reproduction and offspring quality without altering mortality in parents or chicks. Compared with organic pairs, conventional pairs yielded smaller chicks at hatching that had a lower body mass index at 24 days old. Additionally, these chicks displayed lower haematocrit when body mass index was higher. Therefore, ingestion of conventional grains by parents resulted in chronic exposure to pesticide residues, even at low doses, and this had detrimental consequences on offspring. These results demonstrate a sublethal effect of pesticide residues through parental effects. The consequences of parental exposure on chicks might partly explain the decline in wild Grey partridge populations, which raises questions for avian conservation and demography if current agrosystem approaches are continued.
    [Gaffard, A., Pays, O., Monceau, K., Teixeira, M., Bretagnolle, V. and Moreau, J. Environmental Pollution, p.120005.]
  • Anticoagulant rodenticide exposure and toxicosis in bald eagles (Haliaeetus leucocephalus) and golden eagles (Aquila chrysaetos) in the United States
    Raptors, including eagles, are geographically widespread and sit atop the food chain, thereby serving an important role in maintaining ecosystem balance. After facing population declines associated with exposure to organochlorine insecticides such as dichlorodiphenyltrichloroethane (DDT), bald eagles (Haliaeetus leucocephalus) have recovered from the brink of extinction. However, both bald and golden eagles (Aquila chrysaetos) are exposed to a variety of other toxic compounds in the environment that could have population impacts. Few studies have focused on anticoagulant rodenticide (AR) exposure in eagles. Therefore, the purpose of this study was to determine the types of ARs that eagles are exposed to in the USA and better define the extent of toxicosis (i.e., fatal illness due to compound exposure). Diagnostic case records from bald and golden eagles submitted to the Southeastern Cooperative Wildlife Disease Study (University of Georgia) 2014 through 2018 were reviewed. Overall, 303 eagles were examined, and the livers from 116 bald eagles and 17 golden eagles were tested for ARs. The percentage of AR exposure (i.e., detectable levels but not associated with mortality) in eagles was high; ARs were detected in 109 (82%) eagles, including 96 (83%) bald eagles and 13 (77%) golden eagles. Anticoagulant rodenticide toxicosis was determined to be the cause of mortality in 12 (4%) of the 303 eagles examined, including 11 bald eagles and 1 golden eagle. Six different AR compounds were detected in these eagles, with brodifacoum and bromadiolone most frequently detected (81% and 25% of eagles tested, respectively). These results suggest that some ARs, most notably brodifacoum, are widespread in the environment and are commonly consumed by eagles. This highlights the need for research to understand the pathways of AR exposure in eagles, which may help inform policy and regulatory actions to mitigate AR exposure risk.
    [Niedringhaus, K.D., Nemeth, N.M., Gibbs, S., Zimmerman, J., Shender, L., Slankard, K., Fenton, H., Charlie, B., Dalton, M.F., Elsmo, E.J. and Poppenga, R. Plos one, 16(4), p.e0246134.]
  • Birds feeding on tebuconazole treated seeds have reduced breeding output
    Drilled seeds are an important food resource for many farmland birds but may pose a serious risk when treated with pesticides. Most compounds currently used as seed treatment in the EU have low acute toxicity but may still affect birds in a sub-chronic or chronic way, especially considering that the sowing season lasts several weeks or months, resulting in a long exposure period for birds. Tebuconazole is a triazole fungicide widely used in agriculture but its toxicity to birds remains largely unknown. Our aim was to test if a realistic scenario of exposure to tebuconazole treated seeds affected the survival and subsequent reproduction of the red-legged partridge (Alectoris rufa). We fed captive partridges with wheat seeds treated with 0%, 20% or 100% of tebuconazole application rate during 25 days in late winter (i.e. tebuconazole dietary doses were approximately 0.2 and 1.1 mg/kg bw/day). We studied treatment effects on the physiology (i.e. body weight, biochemistry, immunology, oxidative stress, coloration) and reproduction of partridges. Exposed birds did not reduce food consumption but presented reduced plasmatic concentrations of lipids (triglycerides at both exposure doses, cholesterol at high dose) and proteins (high dose). The coloration of the eye ring was also reduced in the low dose group. Exposure ended 60 days before the first egg was laid, but still affected reproductive output: hatching rate was reduced by 23% and brood size was 1.5 times smaller in the high dose group compared with controls. No significant reproductive effects were found in the low dose group. Our results point to the need to study the potential endocrine disruption mechanism of this fungicide with lagged effects on reproduction. Risk assessments for tebuconazole use as seed treatment should be revised in light of these reported effects on bird reproduction.
    [Lopez-Antia, A., Ortiz-Santaliestra, M.E., Mougeot, F., Camarero, P.R. and Mateo, R., 2021. Environmental Pollution, 271, p.116292.]
  • Incidence of organochlorine pesticides and the health condition of nestling ospreys (Pandion haliaetus) at Laguna San Ignacio, a pristine area of Baja California Sur, Mexico.
    Researchers identified and quantified organochlorine (OC) pesticide residues in the plasma of 28 osprey (Pandion haliaetus) nestlings from a dense population in Laguna San Ignacio, a pristine area of Baja California Sur, Mexico, during the 2001 breeding season. Sixteen OC pesticides were identified and quantified. a-, ß-, d- and ?-hexachlorocyclohexane, heptaclor, heptachlor epoxide, endosulfan I and II, endosulfan-sulfate, p,p'-DDE, p,p'-DDD, aldrin, dieldrin, endrin, endrin aldehyde, and endrin ketone were the OCs found in the plasma of nestlings, ranging from 0.002 to 6.856 pg/µl (parts per billion). No differences were found in the concentration of pesticides between genders (P > 0.05). In this work, the concentrations detected in the plasma were lower than those reported to be a threat for the species and that affect the survival and reproduction of birds. The presence of OC pesticides in the remote Laguna San Ignacio osprey population is an indication of the ubiquitous nature of these contaminants. OCs are apparently able to travel long distances from their source to the study area. A significant relationship between hemoglobin and mean corpuscular hemoglobin concentrations and OC concentrations were found suggesting that a potential effect on the health of chicks may exist in this osprey population caused by the OC, e.g. anemia. The total proteins were positively correlated with a-BHC, endosulfan I, and p,p'-DDD. It has been suggested that OC also affects competitive interactions and population status over the long term in vertebrate species, and these results could be used as reference information for comparison with other more exposed osprey populations.
    [Rivera-Rodríguez LB, Rodríguez-Estrella R. 2011. Ecotoxicology.;20(1):29-38]
  • Flame retardants and organochlorine pollutants in bald eagle plasma from the Great Lakes region
    Study reports measurements of polybrominated diphenyl ethers and of emerging flame retardants in the plasma of nestling bald eagles sampled from early May to late June of 2005. Concentrations of total PBDEs ranged from 0.35 ng g(-1) ww to 29.3 ng g(-1) ww. Several emerging flame retardants, such as pentabromoethylbenzene (PBEB), hexabromocyclododecanes (HBCDs), and Dechlorane Plus (DP), were detected in these samples. Polychlorinated biphenyls (PCBs) and organochlorine pesticides were also detected at levels close to those previously published. A statistically significant relationship was found between total PBDE concentrations and total PCB and p,p'-DDE concentrations, suggesting that these compounds share a common source, which is most likely the eagle's food.
    [Venier M. et al. 2010. Chemosphere.80(10):1234-40]
  • Concentrations in bird feathers reflect regional contamination with organic pollutants
    Feathers have recently been shown to be potentially useful non-destructive biomonitoring tools for organic pollutants. However, the suitability of feathers to monitor regional variations in contamination has not been investigated until now. Here concentrations of organic pollutants were compared in feathers of common magpies (Pica pica) between urban and rural areas in Flanders, Belgium. The results showed that concentrations of p,p'-dichlorodiphenyldichloroethylene (DDE) were significantly higher in the rural areas, while polychlorinated biphenyls (PCBs) were significantly more available in an urban environment. This pattern agrees with previous studies using other tissues than feathers as a biomonitoring tool. In addition, differences in PCBs and PBDEs profiles were found with lower halogenated congeners being more prominent in the urban areas in comparison to the rural areas. In summary, feathers seem to reflect regional variations in contamination, which strengthens their usefulness as a non-destructive biomonitor for organic pollutants.
    [Jaspers VL, Covaci A, Deleu P, Eens M. 2009. Sci Total Environ;407(4):1447-51]
  • Chiral organochlorine contaminants in blood and eggs of glaucous gulls (Larus hyperboreus) from the Norwegian Arctic.
    Glaucous gulls (Larus hyperboreus) and their eggs from Svalbard (Norwegian Arctic) have been used as biomonitors of contaminants in the marine environment. In this study, the enantiomer fractions (EFs) of chiral chlordanes and atropisomeric polychlorinated biphenyl (PCB) congeners were determined in the blood plasma of adult male and female glaucous gulls from three breeding colonies in Svalbard. Plasma EFs were similar in magnitude and direction to EFs previously reported in glaucous gulls from other arctic food webs, suggesting overall similarities in the biochemical processes influencing the EFs of bioaccumulated organochlorine (OC) contaminants within the food webs at those locations. Additionally, EFs in yolk of eggs collected concurrently from within the same nesting colonies varied with location, laying date, and OC concentrations, and may be influenced by changes in the local feeding ecology between those colonies. The use of eggs as a valuable and noninvasive means of OC biomonitoring may also extend to enantiomer compositions in glaucous gulls, and perhaps also in other seabird species from arctic regions.
    [Ross MS, Verreault J, Letcher RJ, Gabrielsen GW, Wong CS. 2008. Environ Sci Technol.;42(19):7181-6]
  • Can predatory bird feathers be used as a non-destructive biomonitoring tool of organic pollutants?
    The monitoring of different types of pollutants that are released into the environment, and that present risks for both humans and wildlife have become increasingly important. In this study, authors examined whether feathers of predatory birds can be used as a non-destructive biomonitor of organic pollutants. Study demonstrates that polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT) and polybrominated diphenyl ethers (PBDEs) are measurable in one single tail feather of common buzzards (Buteo buteo) and that levels in this feather and internal tissues are significantly related to each other. Findings provide the first indication that feathers of predatory birds could be useful in non-destructive biomonitoring of organic pollutants, although further validation may be necessary.
    [Jaspers, V,L. et al. 2006. Biol. Lett. 2, 283-285]
  • Can predatory bird feathers be used as a non-destructive biomonitoring tool of organic pollutants?
    The monitoring of different types of pollutants that are released into the environment, and that present risks for both humans and wildlife have become increasingly important. In this study, authors examined whether feathers of predatory birds can be used as a non-destructive biomonitor of organic pollutants. Study demonstrates that polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT) and polybrominated diphenyl ethers (PBDEs) are measurable in one single tail feather of common buzzards (Buteo buteo) and that levels in this feather and internal tissues are significantly related to each other. Findings provide the first indication that feathers of predatory birds could be useful in non-destructive biomonitoring of organic pollutants, although further validation may be necessary.
    [Jaspers, V,L. et al. 2006. Biol. Lett. 2, 283-285]