Range Expansion of the Tree Swallow, 



Tachycineta bicolor (Passeriformes: Hirundinidae), 



in the Southeastern United States 



David S. Lee 



North Carolina State Museum of Natural Sciences 



P.O. Box 27647 



Raleigh, North Carolina 27611 



ABSTRACT— Since the late 1800s and early part of this century 

 when the tree swallow, Tachycineta bicolor, was a peripheral and 

 sporadic breeding species in the southeastern United States, its range 

 has expanded considerably. The precise reasons for the range expan- 

 sion of this and other swallows in the Southeast is unclear. Land 

 clearing, impoundments and other land use patterns, the re-introduc- 

 tion of beavers {Castor canadensis), and the use of bluebird (Sialia 

 sialis) boxes by swallows as nest sites appear to have facilitated 

 the expansion. Several different corridors of dispersal are noted; North 

 Carolina represents the current frontier of range expansion in the 

 Southeast. 



The 1957 edition of the American Ornithologists' Union Check- 

 list (AOU 1957) stated that the breeding range of the tree swallow 

 (now Tachycineta bicolor) extended south to northwestern Tennessee, 

 northern West Virginia, Virginia, central Maryland, and northeastern 

 Pennsylvania. At the turn of the century the species rarely nested as 

 far south as southwestern Kentucky (Fig. 1). The breeding range has 

 expanded considerably since the 1950s, but this change in distribution 

 is not well documented. By the early 1980s the southern limits of 

 distribution were defined as northeastern Louisiana, westcentral Missis- 

 sippi, Tennessee, and North Carolina, but the tree swallow was 

 "generally sporadic or irregular as a breeder east of the Rocky Mountain 

 states and south of the upper Mississippi and Ohio Valleys, or along 

 the Atlantic coast south of Massachusetts" (AOU 1983). 



At least in parts of the Southeast, tree swallows are currently 

 undergoing a rapid range expansion and indications are that they will 

 become common and widespread throughout much of the area during 

 the coming decades. This pattern of range expansion has already been 

 exhibited by several other species of swallows in the Southeast. The 

 majority of the information presented here is from North Carolina, 

 which is the current frontier of range expansion in the Southeast. 



Brimleyana 18:103-113, June 1993 103 



