216 PROPAGATION OF WILD BIRDS 



Proportions Not Important. The matter of the exact 

 proportion of the box thus constructed does not appear to 

 be important. The main requirement is that the cavity 

 or chamber should be fairly deep, with a circular entrance- 

 hole just below the top. Only martins like the entrance near 

 the floor level, though wrens also will use it thus if necessary. 

 Most birds which use hollows for nests like to get out of 

 sight, and perhaps also out of draughts. 



Direction of Axis. The preponderance of practice is to 

 make boxes with the long axis vertical, having them about 

 twice as long as wide. This is the general shape of the 

 hollow-log type of the Von Berlepsch model. In fact, a 

 box made thus of weatherbeaten boards looks considerably 

 like that type . Experience, however, shows that birds will 

 use a square box, or even one slightly elongated horizontally. 

 E. H. Forbush has of late been building his square. On the 

 Henry Ford Farm, near Detroit, where a couple of hundred 

 of boxes are put up and mostly occupied, a good many of 

 them, especially those used by bluebirds, are nearly square, 

 but slightly longer horizontally. My own theory is, from 

 observation of hundreds of natural nesting-sites, that this 

 class of birds usually select a cavity where their nest fills 

 the entire space at the bottom. They also want to be well 

 below the entrance-hole. Hence I would have the floor 

 space of moderate size, preferably about square or round, 

 and the upright dimension rather long. 



Building a Box. As a typical case, here is a plan for 

 making a nesting-box of the size for bluebirds : Saw out four 

 pieces of f-inch board a foot long and 6 inches wide. In 

 one of these cut out a circular hole, the top of which should 

 come about 4 inches from the end of the board. This hole 

 should be i^ to if inches in diameter, no more or no less, 

 because if more the starling can get in, and if less the blue- 



