AIDS TO NESTING 221 



other species nesting in shrubbery might use such a model 

 as the latter, but this yet remains to be demonstrated. On 

 the Henry Ford place robins and phoebes nest in these open- 

 sided boxes or roofed platforms. These can well be fastened 

 to the eaves of buildings or to arbours, piazzas, or against 

 trunks of trees as much protected against cats as possible. 



Size of Entrance. In the matter of the size of the en- 

 trance-hole it is important to be very exact, especially in 

 reference to protecting certain species using boxes from 

 the entrance of the EngUsh sparrow and the European 

 starhng. These are pests to the native species, and some 

 sizes of boxes can be made with reference to keeping them 

 out. Here are the facts: The sparrow can enter a ij-inch 

 opening, but not the if-inch size. The starling can get 

 through the if-inch size, but not the if-inch. T. Gilbert 

 Pearson told me that this had been ascertained about the 

 starling, and I verified it by further experiments. The 

 bluebirds can Just enter a hole i J inches in diameter. Hence, 

 to protect it from the assaults of the starhng, the diameter 

 of the hole should be from i J to if inches, no less or no more. 

 Most species, however, cannot thus be protected from the 

 sparrows, except the wrens and perhaps the chickadee. The 

 wren can enter even a |-inch hole, but the opening may as 

 well be 1 1 inches, so that possibly the chickadee may also 

 have a chance. However, while the chickadee can enter 

 this, Mr. Forbush thinks that it prefers the ij-inch, as he 

 has seen one trying to enlarge a i|-inch hole. In some lo- 

 cahties, as in parts of eastern Massachusetts, the house 

 wren is scarce or absent, and boxes with a very small aper- 

 ture are apt to remain unused. In such case it is probably 

 best to adopt the bluebird size as the general type for all the 

 smaller birds, and make up one's mind to fight the English 

 sparrow. 



