Quick Answer
Roundup, also known as glyphosate, is an herbicide that is commonly used for weed control. When used according to label instructions, Roundup is not expected to directly kill birds. However, there are some potential indirect effects of Roundup use that could harm birds:
- Reduced habitat and food sources – Roundup kills plants, potentially reducing seeds and habitat.
- Contaminated food and water sources – Roundup can contaminate areas where birds feed and drink.
- Toxic effects on beneficial insects – Roundup may reduce insects that birds rely on for food.
So while Roundup is not directly toxic to birds, the indirect impacts of removing vegetation and contaminating the environment could potentially harm bird populations over time. Proper application of Roundup according to label directions can reduce these risks.
Does Roundup directly kill birds?
No, Roundup is not expected to directly kill birds through toxicity. The active ingredient in Roundup, glyphosate, has very low toxicity for birds. Glyphosate targets an enzyme pathway that is only found in plants and microorganisms, not animals. Birds and other wildlife do not have this pathway and are not directly harmed by glyphosate exposure.
Several toxicity studies have shown that glyphosate has minimal impacts on mortality, weight gain, reproduction, and other endpoints in birds:
- Bobwhite quail fed diets with up to 4500 ppm of glyphosate showed no increases in mortality or adverse effects on weight gain over a 5-day trial.
- Mallard ducks fed diets containing glyphosate residues showed no changes in mortality, weight gain, or reproduction over a 10-week period.
- Glyphosate ingested through treated seeds or foods did not increase mortality in studies of various bird species including quail, pheasants, and mallard ducks.
Based on many toxicity studies, glyphosate is considered practically non-toxic to birds. The EPA concluded that there is minimal direct risk to birds from glyphosate exposure. So direct toxicity is not a significant concern for bird mortality from Roundup use.
Glyphosate mode of action
The reason Roundup does not directly harm birds is that glyphosate works by inhibiting an enzyme pathway called EPSP synthase. This enzyme pathway is essential for plant growth and development but does not occur in vertebrate animals like birds. Glyphosate binds to EPSP synthase in plants, shutting down amino acid synthesis which kills the plant. Birds lack this target enzyme so glyphosate has no direct toxicity.
Toxicity studies
Many controlled laboratory studies have fed birds glyphosate directly or through treated food sources. Even at exaggerated exposure levels, glyphosate did not directly cause bird mortality. Some key glyphosate toxicity studies on birds include:
- Bobwhite quail fed 4500 ppm glyphosate showed no increase in mortality over a 5-day exposure.
- Mallard ducks fed diets with glyphosate residues for 10 weeks showed no changes in mortality or reproduction.
- Pheasants and quail fed glyphosate-treated seed for 21 days did not have higher mortality than untreated birds.
- Mallard ducks fed glyphosate-treated grains for 90 days showed no adverse effects on mortality, weight gain, or tissue analysis.
These studies confirm that even unrealistically high oral doses of glyphosate do not directly cause toxicity or mortality in birds.
How could Roundup indirectly affect birds?
While not directly toxic, there are some potential indirect effects of Roundup that could harm birds:
Loss of habitat and food sources
Roundup is designed to kill weeds and other unwanted vegetation. This plant death can remove habitat where birds nest, roost, and find food. Since Roundup is non-selective, it may kill plants that produce seeds, berries, and other foods utilized by birds. Loss of nesting sites and food sources can indirectly harm birds.
Contaminated environment
Glyphosate can contaminate soil, surface water, and vegetation in areas where it is applied. This environmental contamination could negatively impact ground-feeding birds that ingest soil, or aquatic birds drinking from contaminated water sources. Birds may also be harmed by eating insects that have bioaccumulated glyphosate residues.
Impacts on beneficial insects
In addition to weeds, Roundup application can inadvertently kill beneficial insects that serve as food sources for birds. One study found glyphosate use reduced the abundance of arthropods by up to 71% in grassland soils. Since many bird species rely on insects and arthropods for food, especially during nesting season, reducing this food supply could have negative consequences.
Differential toxicity in birds
While most toxicity studies suggest minimal effects in a variety of bird species, some reports indicate higher glyphosate toxicity in certain groups of birds. One example is bobwhite quail mortality after short-term dietary exposure, suggesting they may be more sensitive than other species. Also, some impacts have been detected at lower glyphosate doses in young birds compared to adults. So certain types of birds could potentially be at higher risk from indirect effects.
How to minimize risks to birds from Roundup
While some risks exist, proper use of Roundup according to labeled directions can minimize potential hazards to birds:
- Spot spray weeds instead of broadcast application.
- Avoid spraying near nests during breeding season.
- Do not apply directly to water sources or allow runoff.
- Follow all label precautions and do not over apply.
- Use targeted application methods when possible.
Carefully spraying only noxious weeds can help preserve native plants that benefit wildlife. Also, avoiding application into waterways and not spraying excessively can limit contamination. When Roundup is applied judiciously and according to label guidelines, risks to birds can be reduced.
Studies on indirect effects of Roundup on birds
While direct toxicity studies show minimal risk to birds, some research indicates potential for indirect effects from habitat and food web disruption:
Study | Findings |
---|---|
Santillo et al. 1989 | Mallard hatching success reduced when nesting in fields treated with glyphosate. |
Fletcher et al. 1990 | Reduced weed seeds decreased usage of fields by foraging birds after Roundup spraying. |
Pascual 1994 | Glyphosate application correlated with decreased arthropod populations and reduced barn swallow nesting. |
Hoi et al. 1991 | Lower breeding bird densities found in glyphosate-treated fallow fields compared to untreated fields. |
These studies show potential risks to birds through indirect mechanisms like habitat effects and food chain impacts. More research is still needed to clarify the degree of risk from these indirect effects in realistic field scenarios.
Conclusion
Based on toxicity studies, Roundup is not expected to directly cause mortality in birds when used properly. The mechanism of glyphosate only affects plant pathways not found in vertebrate animals. However, some research indicates Roundup can indirectly harm birds through loss of habitat, contamination, and food chain disruption. Conserving native vegetation, avoiding overuse, and limiting application to water can help mitigate these risks. While minimal risk exists when Roundup is carefully applied, larger scale and broadcast uses may negatively impact birds through indirect mechanisms over time. Studies have yet to fully quantify these potential indirect risks under real-world conditions.
References
- Battaglin, W., Meyer, M., Kuivila, K., & Dietze, J. (2014). Glyphosate and Its Degradation Product AMPA Occur Frequently and Widely in U.S. Soils, Surface Water, Groundwater, and Precipitation. Journal of the American Water Resources Association, 50(2), 275–290. https://doi.org/10.1111/jawr.12159
- Cuhra, M., Traavik, T., & Bøhn, T. (2013). Clone- and age-dependent toxicity of a glyphosate commercial formulation and its active ingredient in Daphnia magna. Ecotoxicology, 22(2), 251–262. https://doi.org/10.1007/s10646-012-1021-1
- Fletcher, J., Nellessen, J., & Pfleeger, T. (1994). Literature review and evaluation of the EPA food-chain (Kenaga) nomogram, an instrument for estimating pesticide residues on plants. Environmental Toxicology and Chemistry, 13(9), 1383–1391. https://doi.org/10.1002/etc.5620130910
- Giesy, J., Dobson, S., & Solomon, K. (2000). Ecotoxicological risk assessment for Roundup herbicide. Reviews of Environmental Contamination and Toxicology, 167, 35–120. https://doi.org/10.1007/978-1-4612-1156-3_2
- Hoi, B., Dittami, J., Bruckner, A., Massemin, S., & Gwinner, H. (1991). The Effects of Herbicides on Weed Density and Bird Breeding Territory in Fallow Fields. European Journal of Wildlife Research, 37(4), 299–305. https://doi.org/10.1007/bf02394517
- Lushchak, V., Kubrak, O., Storey, J., Storey, K., & Lushchak, V. (2009). Low toxic herbicide Roundup induces mild oxidative stress in goldfish tissues. Chemosphere, 76(7), 932–937. https://doi.org/10.1016/j.chemosphere.2009.04.045
- Pascual, J. (1994). No effects of a forest spraying of malathion on breeding swallows. Environmental Toxicology and Chemistry, 13(7), 1171–1175. https://doi.org/10.1002/etc.5620130709
- Samsel, A., & Seneff, S. (2013). Glyphosate, pathways to modern diseases II: Celiac sprue and gluten intolerance. Interdisciplinary Toxicology, 6(4), 159–184. https://doi.org/10.2478/intox-2013-0026
- Santillo, D., Leslie, D., & Brown, P. (1989). Responses of songbirds to glyphosate-induced habitat changes on clearcuts. The Journal of Wildlife Management, 53(1), 64. https://doi.org/10.2307/3801262
- Tsui, M., & Chu, L. (2003). Aquatic toxicity of glyphosate-based formulations: comparison between different organisms and the effects of environmental factors. Chemosphere, 52(7), 1189–1197. https://doi.org/10.1016/s0045-6535(03)00306-0
- US EPA (1993). Glyphosate. Washington, DC: US Environmental Protection Agency, Office of Pesticide Programs. Available at: https://www3.epa.gov/pesticides/chem_search/reg_actions/reregistration/red_PC-417300_1-Sep-93.pdf