BIRDS OF THE UNITED STATES. 
81 
circumscribed cavity is stuifed with fine soft grass, and is warmly lined with 
downy feathers. The average height and breadth of such structures when 
placed on the horizontal rafters of barns is about five inches. The cavity 
is usually three inches wide at the rim — thus making the thickness of the 
walls an inch — and about two inches in depth. When placed against the 
side of a house or of a barn, a strong foundation of mud is usually built, 
upon which the nest is reared. In that event, the nest is more comj)actly 
made, and varies from the preceding by its more elongate form. 
A striking peculiarity of many of these fabrics, is an additional plat- 
form which is placed against the nest proper, but wholly distinct therefrom. 
This is undoubtedly designed as a roosting-place, and is used during the 
incubating period by the one or the other parent at night, or when not 
occupied in the procurement of food, or by both when the young have 
complete possession thereof. 
A nest before us which was built upon a horizontal rafter underneath 
an overshoot, and which may be regarded as typical in the ordinary sci- 
entific sense, is composed externally of ten semi-elliptical series of mud 
pellets, slightly overlapping each other after the manner of tiles, and 
intercalated with the stems and blades of fine grasses. Similar vegetable 
materials are found in small quantities on the outside, which serve to 
strengthen the pellets, thus acting as substantial girders to the entire 
structure. On the inside is a small layer of the stems of our common 
timothy grass, which is followed by another of greater compactness, and, 
finally, by a lining of soft meadow grass. The entire length of this nest 
is four inches, and it gradually tapers from above downwards, giving the 
appearance of a longitudinal section of an inverted cone. The depression 
is two and a half inches wide in one direction, about four in the line of 
greatest width, and scarcely an inch in depth, the shallowness being com- 
pensated for by the greater length transversally. 
The Plate represents a nest which is nearly the exact counterpart of 
the one just described, differing immaterially therefrom in the lack of 
