80 



NORTH AMERICAN FAUNA 69 



was outside the breeding range of the cowbird, but it is gradually 

 extending its breeding range into that area (Webb and Wetherbee 

 1960, p. 83-87). The cowbird is a common breeding bird through- 

 out the lower Mississippi Valley and Appalachian mountains 

 nesting range of the Swainson's Warbler. 



Since one of the choice nesting sites of the Swainson's Warbler 

 in the Coastal Plain is the river floodplain forest, production is 

 markedly limited when such areas become inundated during the 

 nesting season. In the Ocmulgee River floodplain of central 

 Georgia, virtually all of the Swainson's Warblers nest within 

 half a mile of the river. This is where the canebrakes are located. 

 Some of the birds nest right up to the river bank. I have seen 

 some Swainson's Warbler territories that were under 12 feet of 

 water. Three out of 10 years that I worked in this area the nesting 

 ground was flooded during May when the Swainson's Warbler 

 was nesting. 



Calhoun (1941, p. 306) found a similar situation in the Hatchie 

 River bottoms in Hardeman County, Tenn. He made the following 

 statement about these conditions : 



If the Swainson's warbler nests in this same type of region, it would be 

 exceedingly difficult to study its nesting habits because such areas are subject 

 to flooding in the spring and early summer. 



In the Coastal Plain part of its range the Swainson's Warbler 

 would probably have a difficult time maintaining its present popu- 

 lation level, not only because of low nesting success, but also 

 because of its narrow habitat requirements. Canebrakes, prime 

 habitat of this species, have disappeared faster than any other 

 bottomland plant community. Habitat has disappeared faster in 

 the lower Mississippi Valley than elsewhere in the range. Very 

 early, rich bottomlands of the lower Mississippi Valley were 

 stripped of their valuable hardwood timber and then cleared and 

 drained for the agricultural use of their highly productive soils. 

 Habitat in the Great Dismal Swamp and some other South 

 Atlantic lowlands has contracted because the deep shade required 

 by this species disappeared with the harvesting of the mature 

 forest. The cut-over areas were drained and reforested with pine. 



It is possible that the Swainson's Warbler can adapt to so- 

 called marginal Coastal Plain habitat better than is suspected. 

 Some occur there, but these usually are bachelor males. But if 

 the Swainson's Warbler ever has to make a last stand it may well 

 be in the Southern Appalachians, where many of them occur in 

 national forests and national parks or in areas unsuitable for 

 agricultural production. 



