SWAMPS AND SHORES 



477 



most important, element, which take advantage of this seasonal food 

 supply. The birds may be attracted also by the relative absence of 

 enemies and the protection from such as are present which is afforded 

 by the bog habitat. The permanent inhabitants of the tundra zone are 

 discussed below (p. 505). There is an almost complete absence of semi- 



Fig. 122. — Jagana, Parra jacana, of South America. After Plate. 



aquatic mammals, since there is no refuge from the severity of winter 

 for them. 



Vertebrate life of the sea coast. — The transition from sea to dry 

 land in tide flats, salt marshes, and, in the tropics, mangrove swamps 

 and forests, offers a third semi-aquatic habitat, much frequented by 

 the types of birds and mammals already discussed, but with a reduced 

 reptile fauna and with amphibians almost totally absent. 



In the mangrove swamps of Florida, for example, one finds the 

 brackish-water fiddler crabs, Uca, abundant. To the south, these are 

 replaced by the West Indian land crabs which burrow into the muddy 



