NESTS AND NEST-BUILDING IN BIRDS 245 



the inner wall, or in other words the diameter, depth, and sym- 

 metry of the " cup," ^^ which are its most constant and valuable 

 characters, especially in the statant nest; (2) The form and 

 treatment of the outer wall which is characteristic of many 

 nests of either type; (3) The arrangement of the materials used 

 in construction, or the way in w^hich they are put together, but 

 it should be noted that our information under this head can 

 never be reliable or complete without careful observations on 

 the builders at work. These several characters are the most 

 important marks of increment nests because the uniformity 

 which they present in all individuals of a given species is very 

 marked, being the result of uniform methods of building. 



The following characters, with notable exceptions, are less 

 constant because subject to a greater number of modifying 

 influences; (4) The kind of materials used in construction, 

 which are commonly, variable, being as a rule draw^n from the 

 nearest source; (5) The size or weight of the nest, which is most 

 constant in the pendent group, but subject to wide variation in 

 nearly all which are supported from below, and (6) finally the 

 position, which is notoriously subject to wide fluctuation in a 

 great number of species. By " position " we mean the kind 

 of support or immediate environment, as w^ell as the point in 

 space, in reference to the surface of the ground, which the nest 

 occupies. 



It will be most convenient to notice the several characters 

 enumerated in inverse order, since the uniformity of the outer 

 and inner walls will be illustrated by specific cases later. (See 

 section 5.) 



Position of the nest. We might say with a degree of truth 

 that adequate support required for a nest in a given case is 

 usually a prime factor in determining its position. To give 

 an immediate illustration: the mourning dove (see fig. i, part i) 

 commonly builds its shallow platform within 10 feet of the 

 ground but at the present moment a pair of this species is occupy- 

 ing a nest at a height of nearly 40 feet. It is placed in the 

 crotch of a maple tree, 15 feet from a house and above the level 



'" It is common to speak of the outer and inner surfaces of a nest as its " walls," 

 which meet at the " rim;" the " inner wall " will often be designated the " cup." 

 There is properly but one wall, the inner surface of which corresponds to the cup. 

 when the word is used in this sense. 



