IV-106 



which enable many species, such as the white-fronted geese, to 

 shift habitats away from estuarine marshes. Other species, such 

 as Canada geese and mallards, have demonstrated even more adapt- 

 ibility, many remaining the entire winter in the freshwater bodies 

 of the Midwest (Figure IV. 2. 8). Many sea ducks feed upon small 

 crustaceans, fish, and insects that are estuarine-dependent. 

 These ducks have not learned to feed on agricultural lands, and 

 tend to migrate to deeper saltwater environments during the 

 winter. 



In summary, while game waterfowl are frequently observed in the 

 estuarine areas, they do not appear dependent upon specific estu- 

 arine conditions. There are some exceptions, such as the American 

 brant, but research has not determined the relationship between 

 altered habitat and declining numbers. 



Ornamental Birds 



» 



Shore and sea birds are a particularly aesthetic attraction among 

 the national fauna. However, they rarely have a direct tangible 

 economic value, except as a component of the natural ecosystem. 

 These birds are generally more dependent upon estuarine conditions 

 than the more mobile waterfowl, and have demonstrated a greater 

 sensitivity to the overall encroachment of man. The saga of the 

 virtually extinct whooping crane is well known and documented; 



