404 BULLETIN 179, UNITED STATES NATIONAL MUSEUM 



that the bank swallows appear in appreciable numbers. It is then 

 that they may be seen in flocks in company with other species of 

 swallows in the vicinity of human habitations but more frequently 

 along the streams and lakes, where at this season more flying insects 

 are there to attract them. During the first two weeks after their 

 arrival they are very erratic in their behavior, and their chief 

 objective is to obtain an adequate food supply. 



After the flocks of swallows break up for their nesting activities 

 the bank swallow is not so much in evidence as the barn, cliff, and 

 tree swallows, which favor nesting sites in or about the barns and 

 houses of man. At this time the bank swallow resorts to the more 

 isolated sections in which its nesting colonies are located. The first 

 preliminary excavations I have noted in Maine were May 12 but it 

 is not until about 10 days later that nest building starts in earnest. 

 By the first of June the colonies are well established. 



Nesting. — The bank swallow with very few exceptions builds its 

 nest at the end of a burrow that it excavates usually near the top of 

 a nearly vertical bank of a lake or stream or that is provided by the 

 excavations of a railway or gravel and sand pits. They exhibit little 

 inclination for human society and have not departed from their primi- 

 tive nesting habit to accept new environmental conditions provided 

 by man, as have the barn, cliff, and tree swallows. So tenacious are 

 they of their method of nest building that large colonies are restricted 

 in their distribution to places where banks or artificial pits of proper 

 material structure for their excavations exist. As would be expected, 

 the bank swallows are most numerous in the glaciated sections of the 

 country where glacial deposits of sand and gravel abound. 



A departure from their nesting in banks of natural deposits is the 

 use of sawdust piles left by lumbering operations. On June 6, 1902, 

 Barrows (1912) saw from a train large numbers of bank swallows 

 about sawdust piles at Ostego Lake, Mich. There were numerous holes 

 in the vertical sides of the sawdust heaps. He was unable to determine 

 definitely whether the holes were occupied by nesting birds but pre- 

 sumed that they were. Bradford Torrey (1903) reports observations 

 of Mrs. Annie Trumbull Slosson made at Franconia, N. H., in the 

 summer of 1902. She saw no less than 20 holes that had been exca- 

 vated in a sawdust pile, and apparently all were occupied by the swal- 

 lows, which were carrying on their usual activities entering and leav- 

 ing the holes as at any other colony. Such a nesting site, however, is 

 likely to prove precarious. 



E. S. Rolfe (Barrows, 1912) found bank swallows nesting abun- 

 dantly in the walls of an abandoned dry well about 15 feet deep. The 

 perpendicular walls were honeycombed with the nesting holes. 



