16 VLULINOVS4AUDUBONABUIOEY Pie 
recorders, parabolic reflectors and Goodman's Axiom 301 speakers, very 
slight variations in bird’s sounds can be recorded, played-back, even 
photographed and scrutinized. 
“Calls and songs may be classified, firstly, according as they are 
Social, Sexual, Domestic or Self-expressive and then according as they 
are Aggressive, Attractive, Contact or Environmental. Thus the call an- 
nouncing an air-borne predator is Social, Environmental and a fleeing 
signal (Armstrong). 
Numerous attempts have been made to enumerate the sound and 
signal repertoires of birds. The Nuthatch uses twelve call-notes and three 
types of songs (Lohrl) and the Chukar Partridge has fourteen adult calls 
(Stokes). With minimal ferreting, readers can easily find numerous reper- 
toires of many other species. The point is, with considerable experience, 
devoted bird enthusiasts might not only identify species by their sounds 
but get to know the bird's attitudes by discerning the same specie’s sound 
differentiations. 
To distinguish subtle differences in the sounds of the same species 
would certainly be the graduate school of birding. And subtle the sound 
differences often are! 
The Black-throated Green Warbler was found to sing two similar 
but distinct songs: Song ‘A’ was described as the “territorial defense” 
song and Song ‘B’ was the “courtship” song in an experiment conducted 
by Morse and aided by Drs. Ficken among others. Isolated on small 
islands such as Hog Island in Muscongus Bay, Maine, the investigators 
found single pairs of these Warblers. There were no neighbors of the 
same species. Data bore out that Song ‘A’ was most infrequent on the 
smaller islands when compared to the numbers and kinds of calls of the 
same species, but from larger islands (with territorial rivals). Too, in an 
experiment conducted by Stevenson, et al—‘Individual Recegnition by 
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