498 ANIMAL LIFE IX THE TOSEMITE 



The Cliff SwalloAv is probably the best known of all our species of 

 swallows because of its common occurrence about human habitations. Orig- 

 inally, as its name indicates, this bird placed its nests on the rocky walls 

 of caiions and on river bluffs, in consequence of which it was correspond- 

 ingly restricted as to local occurrence. With man's erection of barns and 

 other rough-walled buildings, the Cliff Swallows took to nesting on these 

 structures and so appeared in many new localities. In addition to extend- 

 ing its local range, it is certain that this swallow, in many parts of the 

 west, has increased in aggregate numbers. 



The Cliff Swallow is the most colonial of our six species of the swallow- 

 family. Wherever found it is represented in some numbers and its nests 

 are placed in the closest sort of mutual proximity. At Pleasant Valley 

 on May 25, 1915, ten or a dozen pairs had their nests on the weather-beaten 

 station house, and near Merced Falls on May 28, the same year, a colony 

 of about 20 pairs was nesting on the undercut walls of a small gully in 

 the prairie. (See pi. 47a.) Near Lagrange on May 6, 1919, an assemblage 

 of fully 75 pairs was busily engaged in constructing nests on the face of 

 a stratified cliff at the side of the Tuolumne River. At the McCarthy 

 ranch east of Coulter\dlle, and at Bower Cave, Cliff Swallow nests were 

 seen on the inside of farm buildings, access to the interior in each case 

 being provided by a large open doorway through which the birds could 

 fly to and from their nests. 



The swallows of the Yosemite section can be divided into three groups 

 according to their manner of nesting. The Rough-winged Swallow nests 

 in a hole in a bank, the Western Martin and the Tree and Violet-green 

 swallows seek natural cavities in trees or, in the latter species, also in rocks, 

 while the Barn and Cliff swallows being skilled masons build elaborate 

 nests outside of any cavity, using mud for structural material. 



The home of the Cliff Swallow is shaped like a gourd or retort, having 

 a rather narrow entrance and expanding basally to accommodate the nest 

 proper. (See pi. 47a.) The structure is built entirely of mud (save for 

 a slight lining of soft fibrous materials) Avhich is gathered and applied 

 wet in the form of small pellets. The building of such a nest is a labor 

 which must extend over several days in order that the basal portion of 

 the nest may dry and thus gain strength to hold the later additions. 

 When a nest is well under construction the observer finds it composed 

 of mud in several stages, from the entirely dry base to the wet, most 

 recently applied, material at the rim. While gathering the small rounded 

 pieces of mud the birds at most barely alight upon the ground, balancing 

 Avith their wings upraised and quivering. As the source of supply for 

 mud is often at some distance from the colony the total amount of energy 

 expended in the construction of a nest by a single pair of birds is con- 



