12 



bellied plovers sometimes are abundant about May 30 in 

 suitable localities on Cape Cod. Where the water of a pond 

 is drawn off late in May, sandpipers and plovers of several 

 species are likely to gather. 



Migrating shore birds seek ponds where the water is low. 



The Nesting Time. 



The species of birds to be found in the nesting season at 

 a given place depend largely on the temperature of the locality. 

 ''The southward distribution," says Dr. C. Hart Merriam, "is 

 governed by the mean temperature of a brief period during the 

 hottest part of the year." The temperature at this time de- 

 pends largely on four factors, — the latitude, the altitude, the 

 amount of moisture, and the character of the forests. Latitude 

 and altitude have the same effect. Other conditions being 

 equal, the mean temperature lowers as we go higher up or 

 farther north. Dr. Merriam has been able, after lotig study 

 and as the result of many exploring expeditions, to divide 

 North America into boreal, austral, and tropical "regions." 

 Massachusetts, largely because of its variations in altitude, has 

 animals and plants of both boreal and austral regions. Dr. 

 Merriam has divided these regions into life zones, — the boreal 

 into the Arctic, Hudsonian and Canadian zones, and "the 

 austral into the transition, upper austral and lower austral 

 zones. The zones of the austral region are again divided. The 

 eastern subdivision of the transition zone is called the Alle- 

 ghanian faunal area, and the eastern division of the upper 



