286 U. S. NATIONAL MUSEUM BULLETIN 211 



usnea moss, sometimes in thick masses, and upon this they build their outside 

 frame-work of twigs, usnea, lichens and occasionally a few dried grasses. In one 

 of the nests in my collection the twigs used were mostly dead hackmetack, in 

 another spruce, while in the remainder, twigs from deciduous trees predominated. 

 This frame-work usually becomes thicker and more substantial as it progresses 

 upward. 



Within this outside frame they construct a well modeled hollow bowl, between 

 five and one-half and six centimeters in depth, and between eight and one-half 

 and nine and one-half centimeters inside diameter. This bowl, which seems to 

 the casual observer to be made of mud, is in reality made of 'duff,' the rotting 

 vegetable matter with which the ground of this region is covered, and which 

 when dried becomes nearly as hard and stiff as papier mache; and shows their 

 interesting adaptability to conditions, as real mud must at this season be hard 

 to find. A cross-section of the nest shows the bowl to be of varying thickness, 

 but averaging between five and ten millimetres, and so pressed into its surrounding 

 frame as to become, when it hardens, a part of it. 



After the bowl has been carefully modeled and smoothed off on the inside, 

 it is lined with fine, long green leaves of grasses that grow in the swamps there- 

 abouts, and is finally topped off with dried grasses and fibres of various sorts, 

 and a few thin, bendable twigs. In recently constructed nests I have found the 

 green lining to be absolutely constant, although as incubation progresses, these 

 grasses, of course, gradually turn brown. The diameter of the nest when finished, 

 just across the outside of the bowl, averages about twelve centimetres, while the 

 diameter of the entire structure, except for a few outreaching twigs, varies from 

 fourteen to twenty centimetres. The usual measurements from foundation to 

 top of bowl are from eight and one-half to nine centimetres. 



Bendire (1895) says that a nest taken in Herkimer County, N. Y., 

 "measures 7 inches in outer diameter by b x A inches in depth; the inner 

 cup is VA inches wide by 2% inches deep. One of these nests will last 

 for several seasons, but a fresh one is usually built every year. These 

 birds are very much attached to their summer homes, returning to 

 them from year to year, and rarely more than two or three pairs nest 

 in one locality; in fact, they are as often found singly." 



Eggs. — The set consists of four or five eggs, and one is deposited 

 each day. Bendire (1895) describes them very well, as follows: "The 

 eggs of the Rusty Blackbird are mostly ovate in shape. The shell is 

 strong, finely granulated, and slightly glossy. The ground color is a 

 light bluish green, which fades somewhat with age; this is blotched 

 and spotted more or less profusely, and generally heaviest about the 

 larger end of the egg, with different shades of chocolate and chestnut 

 brown and the lighter shades of ecru, drab, and pale gray. The 

 peculiar scrawls so often met with amomg the eggs of the Blackbirds 

 are rarely seen on these eggs, which are readily distinguishable from 

 those of the other species." 



In a series of 50 sets, reported to me by A. D. Henderson, of 

 Belvedere, Alberta, there are 25 sets of five eggs and 3 sets of six. 



The measurements of 50 eggs average 25.8 by 18.6 millimeters; the 



