26 THE AUDUBON BULL Ea) 
not the targets of the pesticides, but because of the persistence of certain 
pesticides in the environment or because of their secondary effects, these 
wildlife species have suffered nearly total elimination. One of the best 
examples is the peregrine falcon which once was found commonly over 
the entire United States. It is now classified as endangered and is found 
mainly in the northwestern U.S. Their hatching success is extremely low, 
in many cases zero. Certain insecticides are blamed because they cause 
the birds to lay thin-shelled eggs which are broken during incubation. 
ALWAYS RARE 
To be sure, there are a few species that have never been common. 
They have never been plentiful because they have very specific habitat 
requirements and, therefore, occupy a restricted range (geographic area). 
The limestone salamander, for example, is found only in Mariposa 
County, California, at the confluence of Bear Creek and the Merced 
River and along tributaries of Bear Creek, only at the altitudes of 1,200 
to 2,500 feet. There are five species in this classification. 
HOW RARE AND ENDANGERED SPECIES GET THAT WAY 
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