NESTS AND NEST-BUILDING IN BIRDS 263 



trates the fixity of such an instinct when definitely established 

 and correlated with other actions. The robin does not inherit 

 the instinct to use mud in nest-building, any more than it 

 inherits the tendency to use weeds, sticks or grass, or the hum- 

 mingbird, lichens, but it is born endowed with tools and with 

 tendencies to use them in a more or less definite manner upon 

 plastic and other materials drawn from its environment, although 

 in this bird certain kinds of material more readily awaken its 

 building responses than others. 



In describing a series of nests of the English merle or black- 

 bird Rennie ^- remarks that the outer framework differs but 

 little from that of the song thrush (Turdus musicus), or mavis, 

 " except in being more massive, as is also the clay lining, which 

 is put on in a very wet state, probably to save the saliva of the 

 bird; but to prevent this moisture from injuring the eggs, it is 

 lined with a thick bedding of dry hay, which in some nests is 

 very neatly worked into the hollow formed by the clay, while 

 in others it is laid less skillfully, and hence the nest is rendered 

 very shallow. In tw^o of the nests in my possession the masonry 

 of the clay is carried around the branch of the bush where they 

 were built, in order to make it fast, which circumstance, as it 

 is not of usual occurrence, shows that the little architect was 

 guided by intelligence akin to rationality, if not identical with 

 it, and not by what is usually called blind instinct." We give 

 this description for the sake of comparisons with the American 

 robin; in our bird the lining is sometimes of green, not dead or 

 dry grass, and is sometimes dispensed with altogether; the 

 lining in all probability has nothing to do with moisture, and 

 though it forms a softer bed for the eggs it is often so slight in 

 the robin as to suggest that it may be only the relic of a period 

 when such nests were built without the aid of the mud cup at all. 



The clay cup of the robin also suggests an interesting varia- 

 tion in a nest of the olive -backed or Swainson's thrush in my 

 possession, ^^ and at the same time illustrates the importance of 

 the study of behavior, as a check to the interpretations of struc- 

 ture. Of the two nests of this species, w^hich I have to describe, 

 one was from a pasture, the other from a peat sw^amp. Let 



"Op. cit., p. 131. 



^^ I am indebted to Miss Cordelia J. Stanwood of Ellsworth, Maine, for this as 

 well as for many' other rare or interesting nests which she has collected in the course 

 of her studies of the bird-life of that region. 



