The following frequently asked questions and answers will help you understand the world of pesticides, pesticide regulation, and the effects of pesticides on birds. For more help, visit our dictionary of pesticide-related terms

What is a pesticide?
What is DDT?

What kinds of pesticides are there?
What are organophosphates and carbamates?
What are rodenticides?
What are herbicides?
What are inert ingredients?
How is pesticide use controlled in the United States?
How are birds exposed to pesticides?
What are acute and chronic exposures?
What are direct effects?
What are indirect effects?

What is a Pesticide
The term pesticide means 'pest killer'.  Pesticides are chemicals designed to kill target organisms deemed to be pests because they can contribute to human diseases (such as malaria), crop destruction, livestock disease, or are household pests like ants and mice.  The Federal Insecticide, Fungicide and Rodenticide Act (known as FIFRA) defines pesticides as ". . . any substance or mixture of substances intended for preventing, destroying, repelling or mitigating any pest, and any substance or mixture of substances intended for use as a plant regulator, defoliant, desiccant."  

Pesticides can take a variety of forms: liquid, powder, gel bait granular etc. Pesticides manufactured in granular form may be subsequently dissolved in spray tanks and applied as liquid.  Others are applied in particle form.  Not long ago these particles were embedded in silica or processed corn cob, both of which are highly attractive to birds.  More recently clay granules have been developed which come in many varieties and can break apart in soil much quicker.  While less attractive to birds due to their lower visibility, these clay granules may adhere to food items and so may be eaten by birds inadvertently. The forms a pesticide takes are generally determined by agronomic and human health concerns - wildlife effects are rarely considered.

What kinds of Pesticides are there?

Pesticides work by disrupting one or more vital, biological processes of the target organism e.g., photosynthesis in plants or blood clotting in mammals.  They can be divided into groups based on the organisms they target.  These include insecticides, rodenticides, herbicides, nematicides, acaricides, and fungicides.  These kill insects, rodents, plants, nematodes, spiders, and fungi, respectively.

What is DDT?
DDT is part of a particular class of insecticides, widely used after WWII, called organochlorines.  DDT is persistent in the environment and accumulates in wildlife, leading to adverse effects such as eggshell thinning.  In 1972, all uses of the organochlorine DDT were cancelled in the US, closely followed by most other persistent chlorinated pesticides.  DDT is still used in six countries in the Western Hemisphere (Argentina, Belize, Ecuador, Guyana, Peru, Mexico). 

What are organophosphates and carbamates?
Organophosphates and carbamates are insecticides.  They are less persistent in the environment than organochlorines such as DDT, but they are generally more acutely toxic to birds.  These chemicals are toxic to the nervous system, and many of them are still used in the United States.

What are rodenticides?
Most rodenticides are often anti-coagulants.  First generation anti-coagulants such as Warfarin cause hemorrhage.  Second generation types bring about neurological and cardio-pulmonary injury in the target organism before the onset of hemorrhage.  Much of the risk of rodenticides to birds comes from secondary toxicity, or the poisoning of a bird that predated poisoned prey.

What are herbicides?
Herbicides act on biochemical pathways specific to plants, for example photosynthesis.  They can act on contact or by root absorption and their effect can be non-systemic (e.g., diquat) or systemic (e.g., glyphosate).  Generally, they are not directly responsible for bird mortalities but declines in bird populations can be attributed to habitat loss and depletion of food resources caused by these chemicals.

What are inert ingredients?
Any given pesticide product contains one or more active ingredient and any number of inert ingredients to enhance the effect of the product.  The active ingredient is the component designed to kill or otherwise harm the target organism and must, by law, be listed on the pesticide label, but inerts can be toxic too, or may enhance the toxicity of the active ingredient, and yet need not be listed on pesticide labels.  In fact, the mixtures of inert and active ingredients are often closely guarded trade secrets. 

How is pesticide use controlled in the United States?
All pesticide use in the US is regulated via a complex system of registration and review, under the auspices of the Environmental Protection Agency (EPA).  The governing legal act for product registration and use is the Federal Insecticide, Fungicide and Rotenticide Act (FIFRA).  The initial version of this act was passed in 1947, for implementation by the USDA.  It required chemicals to be registered but provided no means of controlling use.  It was not until 1972 that amendments were made to FIFRA to provide mechanisms for risk-benefit analysis and use restrictions, with control handed over to the newly formed EPA. Today, chemical manufacturers bear the burden of proposing new chemicals, testing their toxicity and presenting the case for their use.  EPA scientists and other staff are responsible for evaluating the manufacturer’s case and making decisions on where and when a chemical may be used and how it should be applied.  The part the U.S. public can play in this procedure is by voicing their concern - an increasing role - which can affect the outcome of an EPA decision. 

How are birds exposed to pesticides?
Birds are rarely the target of pesticide application but are often caught in the crossfire of a never ending war between humans and pests.  Peregrine Falcons were nearly wiped out due to DDT poisoning throughout the 50s and 60s.  In 1996 it is estimated that over 20,000 Swainson's hawks, 8% of the species, died in Argentina from 1995-96, due to poisoning by the insecticide monocrotophos (Azodrin, Nuvacron) and the EPA estimated that a single carbamate, carbofuran (Furadan) killed two million birds or more each year in the early 1990's.
Birds are, by their very nature, mobile creatures and cannot usually be kept out of areas where pesticides are applied.  Their ability to cover large distances in a short period of time increases their susceptibility to pesticide exposure.  Birds can come into contact with pesticides by three Routes of exposure:

1. Ingestion
2. Inhalation
3. Dermal absorption

Simply because a bird does not feed on vegetation or insects which have been the target of pesticide application (primary exposure), does not mean that it cannot come into contact with that chemical.  Predatory or scavenging species may be exposed when they feed on target or non-target vertebrate species (e.g., rats) that have themselves been exposed.  This is called secondary exposure.  Runoff or wind can carry pesticides to nearby ponds and fields where birds feed, bathe, drink or gather tainted brush or mud for their nests.

What are acute and chronic exposures?
When we think of birds being affected by pesticides, the image conjured up in many minds is of media headlines citing mass mortalities, accompanied by graphic pictures of fields of dead birds.  In reality, while these do occur from time to time, actual effects may be much more subtle and hard to isolate.  Others may cause species numbers to decline indirectly by weakening the animal or reducing food supply, and others still may reduce species numbers without killing individuals, by reducing breeding success.
Exposure can be either acute or chronic;

• Acute: These are sudden, short exposures to high levels of pesticides.  Acute exposure to organophospates often leads to death of the bird within 30 minutes after symptoms of feather fluffing, labored breathing, muscle tremors and convulsions.
• Chronic: these are defined as long-term exposures.  The problem with these exposures is that because the poisoning takes place over a prolonged period birds are more likely to become scattered over a wider geographical area and may never be seen.  If they are recovered it is much harder to correlate the death with specific pesticide applications.

What are direct effects?
Effects from acute exposures can be immediate or delayed.  Chronic exposure, by definition produces delayed effects. Both types of exposure lead to a range of potential DIRECT EFFECTS, which might be lethal or sub-lethal:

• Lethal: in addition to the highly visible mass mortalities, birds can die in a variety of other ways due to pesticides, from both acute and chronic exposures.  Again, the slower the reaction, the harder it can be to detect.
• Sub-lethal:
• Weakening: If a bird is hit by a car, we might simply put that down to bad luck for the bird or careless driving by the driver.  But if the bird's vision or reactions are impaired by chronic exposure to pesticide it is neither.   Birds that are suffering from pesticide poisoning are more likely to be killed by predators. 
• Reproductive: these effects include egg shell thinning (as was the case with DDT), deformed embryos, reduced fertility and decreased hatchability of fertile eggs.  Most of these effects are never seen unless specifically.  Fertility reduction is only noticeable when looked at over successive generations.
• Behavioral:  these changes are perhaps the most subtle of all potential pesticide effects.  Changes in territoriality, vocalization, courtship and breeding behaviors, reduced attention to young and a reduced response to human presence may all result after pesticide exposure, with latent effects on individuals or populations.

What are indirect effects?
Birds that use roadside margins or hedgerows for nesting, roosting, cover or food can decline when these areas are 'cleaned up' by civic authorities' 'beautification' programs.  Birds will likewise be affected if their primary food source is also regarded as a pest or is a non-target species that is affected nonetheless by insecticide or herbicide application.  While the pesticide does not necessarily poison the bird, it is nevertheless the indirect effects of the chemicals that are ultimately responsible for reduction in populations.  In addition to the effects on birds to direct exposure to pesticides, birds can be affected by the pesticide without ever coming into contact with it.  These are called Indirect Effects.