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Bird - Lore 



of the structure which produces it, for the vocal apparatus of some of the 

 lower orders is more complicated in some ways than that of the true songsters. 

 The voice of birds is not produced in the larynx as it is in man, but in a 

 structure called the syrinx, which is located at the opposite end of the trachea, 

 where it divides into the bronchial tubes. Here are located the membranes 



which vibrate, as do the vocal chords of 

 mammals, to produce the sounds. Without 

 going into details of structure, it might be 

 mentioned here that in the true singing birds, 

 called oscines, these membranes are con- 

 trolled by from five to seven pairs of muscles, 

 while in the lower families the number of 

 controlling muscles is less. The sounds are 

 produced entirely by the air rushing past 

 these membranes, causing them to vibrate, 

 the rapidity of the vibrations and the cor- 

 responding sounds produced being controlled 

 by the tension of the muscles. Undoubtedly 

 the larynx and the tongue more or less 

 modify the sounds, if we can judge from 

 their motions during singing. There are, 

 however, among the higher families, no 

 sounding-boards such as are developed, for 

 example, in the trachea of the male ducks. 

 The syrinx of a male duck is a curious 

 looking object because of the great shell-like 

 swelling of the lower end of the trachea, 

 which gives resonance to the mating-call. In 

 addition, certain species have accordion-like enlargements of the middle of 

 the trachea, features which are never developed among the true songsters. 



The song of birds, like the bright plumage of many, is undoubtedly a 

 secondary sexual character, and has been developed as a means of bringing 

 the sexes together. As one might expect, therefore, it is best developed in the 

 males and largely confined to them. The females of a few species, however, 

 occasionally sing nearly as well as the males, but their songs are usually much 

 more subdued. Female Cardinals, Rose-breasted Grosbeaks, and Purple 

 Finches are noted for their vocal ability, and a number of tropical American 

 Wrens sing delightful little duets with their mates. (See 'Impressions of the 

 Voices of Tropical birds' by L. A. Fucrtes, November-December, 1913, Bird- 

 Lore.) 



Song is usualb mm militant with the breeding season. With some birds, 

 like the Red-winged Blackbirds and the Warblers, it begins with the north- 

 ward movement in the spring, and they are singing their full songs when they 



HOUSE WREN SINGING IN 

 CHARACTERISTIC POSE 



