72 



NORTH AMERICAN FAUNA 69 



of song delivery of several other parulids as follows: Yellow 

 Warbler (Dendroica petechia), 11.2 seconds; Prairie Warbler, 

 12.9 seconds; Ovenbird, 21.2 seconds; and Hooded Warbler, 9.8 

 seconds. 



Some of the factors that influence the rate of singing are the 

 stage of the reproductive cycle, time of day, and degree of ex- 

 citement. During the nest-building period one male Swainson's 

 Warbler had an extremely rapid cadence of 4 seconds early in 

 the morning (at 6, 6:30, and 6:35 a.m.). He was signaling his 

 mate, which at the time was building the nest. The course, or 

 series, was short in each case, containing only four to six songs. 

 On each of the three occasions, the female discontinued nest 

 building and flew to her mate, a distance of about 100 feet. 



Comparison with associates 



On hot June days in the Dismal Swamp, I found the Swainson's 

 Warbler to be one of the most frequent singers in the woods if it 

 had an active nest or fledged young in its territory. The Red-eyed 

 Vireo (Vireo olivaceus) sang more continuously, but its song did 

 not stand out like that of the Swainson's Warbler. In the early 

 afternoon when song activity is generally at a minimum for most 

 birds, the Swainson's Warbler often was the most persistent 

 singer. On July 8, 1967, a Swainson's Warbler was the only 

 species that I could hear singing during a driving rainstorm. 



I have to disagree generally with Brewster (1885a, p. 72) who 

 says that the Swainson's Warbler is a "fitful and uncertain 

 singer" and that "you may wait for hours near his retreat, even 

 in early morning, or late afternoon, without hearing a note." I 

 have noted such behavior in many species of birds, but it may 

 result from particular conditions at the time of observation. If 

 one visits a Swainson's Warbler territory daily in the early part 

 of the breeding season before pairing, it will soon be observed 

 that this warbler sings as frequently as most of the other wood- 

 land birds. Frequency of singing, as pointed out above, depends 

 on the stage of the breeding cycle, the time of day, and the 

 meteorological conditions, among other factors. Between the for- 

 mation of the pair bond and nesting, they sing very little. 



ALARM OR CALL NOTE 



Next to the primary advertising song, the chip or tchip note, 

 given by both sexes, is the best known vocalization of the Swain- 

 son's Warbler. The chip note is sharper than the similar note of 

 the Kentucky Warbler, an associate in much of the Swainson's 

 Warbler breeding range. To me, the Swainson's Warbler chip is 



