The Effects Of Pesticides On Wildlife

Pesticides affect a broad range of species in a wide variety of ways. Effects can be immediate and lethal, or long-term and sub lethal.

Pesticides can act directly, by poisoning, by affecting the hormone system, and so on, or indirectly, by altering a species' habitat or food supply. While the first casualties will be those species in the immediate area where the pesticides were applied, such as beneficial insects, the effects will not necessarily end there.

Pesticides move in the environment, and often persist over long periods of time, and therefore species outside of the targeted area will be affected.  Some of the key species we need to worry about are bees, birds, amphibians, and fish.

Bees

Bees are very important insects because they act as pollinators, which is important for biodiversity and for agricultural production. Bees recover slowly from insecticide spraying and other disturbances because of their low fecundity (they are unable to reproduce rapidly or in great numbers) which also makes them more susceptible to local extinction.

For more information on pesticides and bees try these websites:

• Bees and Pesticides (WLAP)
• Pollinators US Fish and Wildlife Service)

Birds

In Canada, more than 30 registered pesticides can poison wild birds. Most of these are the cholinesterase-inhibiting organophosphates and carbamates. Mammals are much better than birds at detoxifying organophosphates and carbamates. For example, birds are 100 times more sensitive than mammals to the organophosphate diazinon, a common active ingredient in many insect sprays. Insects and vegetation sprayed with insecticides can contain sufficient residues to kill birds. Sublethal effects can also occur, as well as such indirect effects as habitat loss and the depletion of food supplies.

For more information on the impacts of pesticides on birds, try these websites:

• Pesticides and Birds Campaign (American Bird Conservancy)
• Pesticides and Wild Birds (Canadian Wildlife Service)
• Pesticides Royal Society for the Protection of Birds)

Amphibians

There is growing evidence that pesticides are partly responsible for dramatic amphibian population declines occurring throughout North America. The consequences of chemical stressors, such as pesticides, on amphibians are lethal, sublethal, direct and indirect. The sublethal affects include hampered growth and developmental and behavioral abnormalities. In turn these abnormalities may increase an amphibian's susceptibility to predation and decrease its reproductive success.

Pesticides also weaken the immune system making amphibians more susceptible to parasites, disease and UV radiation. Certain pesticides can disrupt the endocrine system, resulting in sexual malformations, such as hermaphroditism (see section on Endocrine Disruption).

For more information on amphibians and pesticides see:

• AmphibiaWeb (UC Berkeley
• Canadian Amphibian and Reptile Conservation Network
• Homeowner's Guide to Protecting Frogs - Lawn and Garden Care (pdf)

Fish

The US Geological Service has found concentrations of pesticides in Pacific Northwest rivers and streams at levels that are associated with negative impacts on fish growth, development, behaviour and reproduction. Pesticides can impair swimming ability, cause abnormal sexual development, and cause skeletal deformities. Indirect affects include reduction in food supply, and reduction or elimination of vegetative cover used by young fish. In BC, and the entire Pacific Northwest, the main concern is for the health of already greatly depleted salmon stocks.

For more information on pesticides and fish see:

• Clean Water for Salmon Campaign (NCAP)
• Clean Water for Salmon Campaign (Washington Toxics Coalition)
• The Quality of our Nation's Waters - Nutrients and Pesticides (USGS)