BIRDS OF THE UNITED STATES. 
19 
measured four inches ; in depth, three inches, and in internal diameter 
three and a half inches — being widest in the middle. Specimens, similarly 
colored, have been frequently observed in Pennsylvania. 
By far the’ most remarkable structure which we have seen is the one 
we are about to describe. This domicile was built in a red or swamp 
maple, at an elevation of nearly thirty feet from the ground. It is a 
double nest, composed entirely of long, flexible, yellow grasses, and securely 
fastened between three nearly vertical branches, in a linear direction. The 
main nest is inversely sub-conical, four inches high, with an external 
diameter of three and a half inches in the middle, and four at the top. 
The diameter of the cavity is three inches, and the dejith two and three- 
fourths inches. The smaller is joined to the first by a continuation of the 
grasses of the latter, is somewhat similarly shaped, but less compact in 
structure. The height is one and three-fourths inches, external diam- 
eter in the long direction three and one-fourth inches, and in the short, 
but two inches. The depth of the cavity is one and three-fourths inches, 
and the width, one and a half inches. In one side there is a circular 
hole one inch in diameter. Various opinions have been ventured as to 
the object of this additional structure. Some have contended that it was 
never intended for occu]3ancy or ornament, hut is simply a fabric which 
the authors have failed to complete. But its comj^leteness and finish operate 
against such a theory. The writer, as well as others who have witnessed 
this curious specimen of mechanism, are convinced that it was erected for 
a special purpose — namely, the accommodation of either parent while the 
other is sitting. The opening alluded to, served for the head of the non- 
sitting bird, who, from his position, looking away from the main building, 
could detect the approach of enemies, like a sentry upon an outpost. 
The nest being completed, on the following day the female begins to 
deposit her complement of three or four eggs, at the rate of one egg daily. 
Incubation now ensues, sometimes on the day of the last deposit, but gen- 
erally on the morrow. This duty lasts from fourteen to fifteen days, and 
is wholly the work of the female. While she is thus occupied, the male 
