BIRD HOUSES AND HOW TO BUILD THEM. 



11 



through it runs a cord by which the house is raised and lowered. 

 The floors are all removable by lifting up. When the house is out of 

 contact with the roof all of the entrances are closed by gates actuated 

 by springs, the gates moving upward to close, and being kept down 

 and open by pressure against the roof. By means of this device spar- 

 rows may be kept out of 

 the house until martins are 

 due to arrive, or if they get 

 in when the house is open 

 they can be trapped by sud- 

 denly lowering it. The pole 

 shown here is made from 

 hardwood boards put to- 

 gether with screws. The 

 concrete base has a core 

 of 2-inch iron pipe which 

 extends upward far enough 

 to make a firm connection 

 with the upper part on 

 which the house slides. A 

 heavy weight is employed to hold the house hard against the roof. 

 By passing the cord around the hook of the weight exactly as shown 

 in figure 39 and pulling it upward until the weight is clear of the 

 ground, it can easily be held without slipping while a more secure 

 knot can be tied. A hook less wearing to the cord and fully as serv- 

 iceable may be made from an acute natural crotch of oak or other 



FIG. 30. Sections of house shown in figure 29. Upper floor 

 removable. 



IO" 



6" * &**<- * 6 W 



FIG. 31. Lumber diagrams for house shown in figure 29. Thickness of boards \ inch. 



hardwood instead of iron. Where this house is exposed to strong- 

 winds it may be advisable to attach guy wires to corners of the roof. 

 The pole may be made of a single piece of 4-inch galvanized pipe, set 

 in a concrete base. In this case the house should be a cylinder and 

 the roof a cone. 



