-38- 



Th e swan, Cygnus columbianus , which as recently as a few 

 years ago fed offshore in shallow water while the less wary 

 geese flew inland to feed on stubble fields, have now begun to 

 emulate the habits of geese and can be seen in flocks of several 

 hundred on fields far from open water. This may be due in part 

 to a decrease in the supply of food offshore resulting from 

 increased turbidity and pollution. Nevertheless, it is difficult 

 to anticipate in which bay or river the overwintering species will 

 concentrate from year to year. 



Setting aside natural areas to accommodate overwintering 

 species is not practical unless the areas are specifically managed 

 for waterfowl, and such management may then interfere with other 

 uses or values of a given area. Even so, unusual concentrations 

 of overwintering waterfowl have been noted and considered as a 

 criterion for natural areas selection. 



Seasonal Br eed ers . Various species of animals concentrate 

 in certain areas to reproduce. This is particularly true of many 

 migratory species of birds and fish and for some mammals and 

 amphibia. Birds nesting in certain areas, e.g., heronries and sea 

 bird nesting sites, may result in very high seasonal populations. 

 Spawning fish, especially anadromous species, concentrate in 

 selected areas during reproduction periods. In Chesapeake Bay, 

 striped bass ( Mo rone saxatilis ) , herring ( Alosa aestivalis ) , 

 hickory shad ( Alosa mediocris ) , white shad and American shad 

 ( Alosa sapidissima ) ascend freshwater streams to breed, many in 



