HOW ANIMALS GET IN NEW AREAS 



301 



other light-loving weeds, brought by means of their wind-blown 

 seeds. With these are found patches of berries, the seeds of which 

 were brought by birds or other animals. A little later, quick- 

 growing trees having seeds easily carried for some distance by the 

 wind, like the aspen, or seeds often distributed by birds, as the wild 



j cherry, invade the territory. 



I Eventually we may have the 



I area retenanted by the same 



I kind of inhabitants as formerly, 



i especially if the destruction of 



j the original forest was not 



I complete. 



In like manner, on the 



! upper mountain meadows or 

 by the sand dunes of the sea- 



■ shore, wherever plants place 



I their outposts, the advance is 

 made from some thickly in- 



: habited area, and this advance 

 is always aided or hindered 



I by agencies outside of the 

 plant — the wind, the soil, 

 water, or animals. Thus the 

 seeds obtain a foothold in new 

 territory, and new lands are 

 captured, held, and lost again 

 by the plant communities. 



How animals get a foothold 

 in new areas. There are 



many ways in which animals spread over new areas. Transporta- 

 tion to quite distant parts may take place, as when polar bears or 

 seals are carried on ice floes long distances or when insects and 

 other small forms like crustaceans and snails may be carried 

 hundreds of miles by ocean currents. Birds may carry encysted 

 microscopic forms or even the eggs of mollusks or crustaceans in 

 little balls of mud which stick between their toes. Man himself 

 may play a very important part in the distribution of animals in 



Frank M. Wheat 



In the giant cactus, woodpeckers drill their 

 nesting holes. In following years, these holes 

 are often used as nests in turn by small owls (elf 

 owls), sparrow hawks, screech owls, fly catchers, 

 and wrens. 



