BUILDING BIRD HOUSES 



669 



Fig. 40. Details of construction and operation of gates. 



is open they can be trapped by suddenly lowering it. The pole shown here is 

 made from hardwood boards put together 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 serviceable may be made 

 from an acute natural crotch of oak or other 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. 



"From a bulletin of the Biological Survey. 



Campers More Careful 



In northern Arizona, Utah, Nevada, southern Idaho, and western Wyoming, the fires on 

 national forests set by campers have decreased in four years from nearly a third to ap- 

 proximately one-fifth. Lightning fires have increased from less than one-fourth to nearly 

 one-half. The relatively larger proportion from lightning, however, is due partly to de- 

 crease in other causes. 



