Effects on the Environment - #5

In article #1 of this series World Bird Sanctuary volunteer, Jennifer Jones, talked about one specific pesticide—rodent poison.  Here she discusses pesticides in a more general overview.

Pesticides cause significant bird mortality each year. Of the five billion pounds of pesticides that are applied worldwide every year, 20% are used in the United States (U.S. Environmental Protection Agency [USEPA], 2004). Approximately 40 pesticides still used in the U.S. are documented to have caused bird die-offs. The U.S. Environmental Protection Agency (the U.S. government agency responsible for regulating pesticides) has recorded more than 1,700 incidents of bird kills - many including hundreds of individual birds - attributable to pesticide use.

 Pesticide effects may be lethal, sublethal, acute, chronic, habitat related, or there may be no effect at all. A sub lethal effect is usually from a repeated exposure to some pesticides and though it does not kill the bird it affects it in other ways.  These effects are hard to detect but nevertheless can produce dramatic species declines over time.  Other effects of sublethal are weakening and behavorial.

An acute effect is a sudden, short exposure to high levels of pesticides.  Responses of birds to acute exposure can vary significantly.  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. Effects from acute exposure can be immediate or delayed. 

Chronic effects 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.  Chronic exposure produces delayed effects.  One such effect is the decrease in breeding success, such as we saw with the pesticide DDT.

Habitat Related effects include loss of seed set or berry production in vegetation if bees are killed by pesticides.  Also, runoff into wetlands reduces the number of aquatic insects essential to the growth and development of aquatic birds.  The use of insecticides on lawns reduces the number of earthworms, which affects the American Robins in particular.

In general, insecticides are more toxic to fish and wildlife than herbicides or fungicides; though some herbicides may harm wildlife by damaging the habitat in which it is found.

Insecticides work by interfering with the central nervous system of insects.  The central nervous systems of fish and wildlife that ingest tainted insects may also be affected.

Wildlife can be exposed to pesticides directly by eating contaminated food or water, breathing pesticides or by skin absorption.  Young birds that are fed infected insects are at great risk of suffering lethal pesticide exposure effects.

One such chemical was banned back in 1972; it was the reason why the Bald Eagle and the Peregrine Falcon were on the endangered species list.  The chemical called DDT caused the eggs that were laid to have eggshells so thin that when the eggs were incubated, they were crushed by the weight of the parent bird.   Since the ban of DDT both the Bald Eagle and the Peregrine Falcon have made a comeback and are no longer on the endangered species list.  This is a prime example that we can right what we have done wrong.

When you purchase any pesticide, be sure to read the label to determine whether it is considered toxic to humans and wildlife.  Most chemicals are now required to state this on the label.

Submitted by Jennifer Jones, World Bird Sanctuary volunteer