provide few of the needs of wildlife. Sanitation cuttings that remove all 

 hollow, dead and dying trees and sprawling nut- and mast-producing 

 hardwoods eliminate the dens, nest sites, and food of many forest 

 species. 



Draining and filling marshes, potholes, and other wetlands to expand 

 croplands, commercial and industrial complexes, and transportation 

 systems pose major threats to waterfowl and other wildlife. Coastal 

 marshes, favorite sites for factories, refineries, and airports, are among 

 the most productive types of habitats for a wide range offish and aquatic 

 wildlife. Channelization can destroy the habitat of animals frequenting 

 rivers and streams. 



FMM AND HIS ACTlVIKe:^ HAVE IMTEPROPTED WILDLIFE^ 

 NATURAL cyCLK AMD SYST1E^AS . 



Livestock grazing can improve conditions for some wildlife, but 

 overgrazing can exclude most wildlife use, often for many years. Large- 

 scale brush-clearing to favor grasses can eliminate food and cover 

 needed by many birds and mammals. 



Modern technology has produced a broad range of pollutants with 

 which wildlife must contend. Some, like certain pesticides and mercury, 

 kill directly. Others, like DDT, operate more subtly on the animals' 

 reproductive systems, cause eggshell thinning in some birds, and de- 

 press hatching success in others. Acid mine wastes and industrial 

 pollutants destroy vegetation essential to the survival of many species. 



These and many other critical environmental problems concern the 

 wildlife manager. Often his recommendations, if applied, can have a 

 major influence on the continued survival of one or more species in a 

 given area and help maintain nature's functioning systems. 



Only through careful guidance of all human activities that affect 

 wildlife, both indirectly and directly, can their populations be assured. 



10 



