NATURAL HISTORY OF THE SWAINSON'S WARBLER 53 



well-spaced and not in a series like constant chipping when the 

 birds seem excited. A paired female sometimes utters a faint zeep 

 when a male in an adjacent territory sings. 



On one occasion a pair that I had under observation was joined 

 by a third bird, presumably a female. The visiting female fed w^ith 

 the pair for about 4 minutes, and at no time was chased by the 

 male. The paired female chipped constantly v^hile the interloper 

 remained. 



Pouncing 



During the mating period males resort to pouncing on the 

 females. The male flies to the female, v^ho usually is foraging on 

 the ground, and either pecks her rump feathers or pounces on her. 

 I observed this behavior for several breeding seasons before I 

 was sure that sometimes copulation was taking place. It was 

 difficult to believe that copulation could occur under such circum- 

 stances. Hann (1937, p. 154) also had difficulty in observing 

 copulation during similar behavior by Ovenbirds on the ground : 



When copulation takes place on the ground, it is practically always accom- 

 panied by a struggle, which looks more like mortal combat than sexual inter- 

 course. The fact that the female does not flee, and may even court the 

 procedure, however, dispels any doubt as to her willingness. When they 

 emerge from the struggle, the male usually flies to a nearby perch with an 

 evident feeling of satisfaction, and the female, after shaking her ruffled 

 feathers, proceeds with her eating or nest building. 



Essentially the same behavior is exhibited by the Swainson's 

 Warbler. 



Pouncing may occur with or without an "invitation" from the 

 female. Most of the time the female appears to be unaware that it 

 is going to happen. Sometimes the female's excited chipping im- 

 mediately preceeds the stalking and pouncing. 



After observing pouncing behavior a few times, I could always 

 anticipate when it was going to happen. The male, feeding on the 

 ground, usually within 20 feet of his mate, discontinued feeding 

 and mounted a branch or log, usually 6 to 12 inches from the 

 ground. Then he remained virtually motionless in a crouched 

 position for 1 to 5 minutes, facing and watching the female who 

 was foraging on the ground or perhaps preening. In his crouched 

 position the flank feathers of the male were slightly fluffed out, 

 and his head was drawn in close to his body. Occasionally he 

 would slowly move his head slightly to one side. When the female 

 moved too far out of range, the male shifted to a closer perch and 

 continued his crouched stance. His performance reminded me of 

 a cat getting ready to pounce on its prey. He would then fly to 



