NATURAL HISTORY OF THE SWAINSON'S WARBLER 49 



' itablished by the male shortly after arrival on the breeding 

 ' rounds may be defended at any time. When the male is not paired 

 ' e uses most of the territory. If the first nest is destroyed, and 

 le male and female become separated before the start of a 

 Bcond nesting attempt, the whole territory may be used. The part 

 sed is smallest during the mating and nest-building periods 

 fig. 21), and sometimes during egg-laying. Stenger and Falls 



POWER LINE 



i'lGURE 21. — Variation in size of the territory of a male Swainson's Warbler 

 during breeding season. Only the hatched area (with densest cover) was 

 occupied during the courtship and mating period. Dismal Swamp in 

 Virginia, April 1969. 



(1959, p. 136) found that the area utilized by Ovenbirds was 

 larger during the premating, mating, incubation, and nesting 

 periods than during nest-building and egg-laying. 



Swainson's Warblers usually occupy larger territorial areas 

 during the first few days after their arrival on the breeding 

 grounds ; and after the nesting season males that remain on their 

 territories may extend the boundaries considerably. A male in the 



IIDismal Swamp that occupied 4.1 acres in May and June occasion- 

 ally extended his range over an 8-acre area in July. 

 The size and shape of a territory changes during each nesting 

 attempt, because a different nest site is chosen each time and the 

 j sites may be several hundred feet apart. The male gives the nest 

 jsite a wide berth when the female is incubating, thus giving the 

 appearance that the nest is out of the territory when actually it is 

 inside near the edge. The part of the territory most frequented by 

 one Dismal Swamp male during a first nesting attempt was 



