66 



NORTH AMERICAN FAUNA 69 



whether I was hearing a Swainson's Warbler whisper song or 

 notes of the other three birds. In fact, the whisper songs of 

 several species of warblers sound alike. I have been fooled by the 

 Prothonotary Warbler and the Yellowthroat (Geothlypis trichas), 

 thinking I was hearing a Swainson's Warbler. 



The whisper song is seldom audible beyond 30 feet. It is given 

 throughout the breeding season. Mayfield (1960, p. 127) thought 

 that the Kirtland's Warbler sang whisper songs mainly when 

 other males were nearby. Morse (1967, p. 497) found that in the 

 Parula Warbler (Parula americana) muted and incomplete songs 

 were associated with a high level of aggression. I have heard the 

 Swainson^s Warbler give the whisper song when in the presence 

 of other males, following a conflict at a territorial border, when 

 alone on an isolated territory, and after pouncing on a female 

 just as she was about to feed fledglings. I have heard the whisper 

 song of the Swainson's Warbler most often when there was no 

 other male or female of the species, or any other bird, nearby. 



The whisper song may be delivered when the bird is standing 

 or moving on the ground, perched on a limb, or in flight. I heard 

 one male give the whisper song as he flew along about 2 feet above 

 the ground for a distance of 50 feet. The whisper and primary 

 advertising songs may be alternated : I observed a perched Swain- 

 son's Warbler that sang both, preening in between, and then 

 hopped to the ground, alternating the songs while foraging. 



Flight song 



I have heard flight songs that had no resemblance to whisper or 

 primary advertising songs. They were as loud as the primary 

 advertising songs but continuous and run together, and they 

 lasted as long as the flight. One singing bird took off from the 

 ground in a spiralling flight to a height of about 35 feet ; another 

 flew from the ground at a 60-degree angle to a perch 40 feet up. 



Incomplete song 



Incomplete songs — songs without endings and songs consisting 

 of only the first, second, or third notes — may be heard at any time 

 during the breeding season. As mentioned above, incomplete 

 songs are sometimes given following territorial bouts with neigh- 

 boring males. They are often heard when a bird is startled or 

 frightened. For example, a Dismal Swamp male alternately sang 

 only one and then two notes when a Common Grackle ( Quiscalus 

 quiscula), a nest robber, invaded his territory. 



SINGING BEHAVIOR 



The primary advertising song is sung only by the male, and so 



