PASSERES TYRANNIDAE C. VIRENS VAR. RICBARDSONI. 355 



a horizontal branch ; and, in one instance, where a large limb had been torn 

 from the tree by the wind, a nest was placed flatly upon a broad board-like 

 splinter. The usual situation, however, was, as I have said, the terminal 

 fork of a horizontal limb ; precisely the place chosen by C. virens. There 

 is considerable difference between the nests of the two Wood Pewees ; but 

 the same style of architecture is apparent in both, and the differences can 

 all be accounted for by local causes. The greater depth in the case of 

 richardsoni is rendered necessary by the prevailing high winds in the West, 

 and the difference in composition is doubtless owing largely to the lack of 

 some materials in the West which the eastern birds employ. Both birds 

 appear to rely more upon artifice than concealment for the safety of their 

 nests. They place them in plain sight, but fasten them neatly to the limb, 

 covering the outside with materials that resemble the bark of the tree. 

 Then, should the discovery of their home seem imminent from some chance 

 passer-by, the owner of the nest retires to a short distance and seems to say 

 ' that is not my nest but merely an excrescence of the tree '; oftentimes, how- 

 ever, the energy with which the assertion is made leads to his betrayal. In 

 the vicinity of Chicago, where I have observed the breeding habits of virens, 

 their nests were shallow, and studded outwardly with lichens, like a Hum- 

 mingbird's nest. In Colorado, the nest of richardsoni is more bulky and 

 a third deeper than that of virens. and no lichens at all arc used in its con- 

 struction, but instead the gray dead leaves of a minute plant that grows 

 abundantly in the mountains is often found upon the outside. The chief 

 basis of the nest is dead grasses, gray and crumbling with age; but the inside 

 is lined with fine, yellow, wiry grass tops. The whole structure is firmly 

 bound together with strong silken fibers, so fine as only to be seen on close 

 examination. Contopus richardsoni breeds abundantly along the streams of 

 the plains at the base of the mountains, and also extends up to timber line. 

 It seems to be indifferent as to the kind of tree on which its nest shall be 

 placed, as I have found them on almost every tree that attains any size in 

 Colorado oak, cottonwood, aspen, cedar, spruce, and pines They also 

 occupy both dead and live branches." 



