44 AMIIUCAX WARBLERS. 



reproductive organs and general debilitation preceding the 

 moulting season. As this weakening is gradual, the song is 

 gradually changed. In other words, a summer scng is only 

 the effort made by the warbler to produce the ordinary song 

 with an impaired musical apparatus. 



Students of bird songs should learn the peculiar intona- 

 tion with which birds render their notes. This intonation is 

 strongly specific and is less affected by either individual vari- 

 ation, or by the weakening of the singing muscles, than any 

 other quality of the song. Some of my pupils who read this, 

 will remember that I called their attention to this intonation 

 one day, late in July, when listening to the summer song of 

 the Black-throated Green Warbler on Prospect Hill, Wal- 

 tham . 



Migration axd Breeding Range. The Black-thrcat- 

 ed Greens breed commonly along the AUeghanies from South 

 Carolina northward, all over New England, north to Hudson 

 Bay, and west to Illinois. 



On the southward migration the greater portion of these 

 warblers leave Massachusetts the last of September, but some 

 remain until the middle of October. 



I h?.ve never seen a specimen in Florida, the Bahamas, or in 

 the West Indies. They winter in Central America. 



On the northward migration they pass through Pennsyl- 

 vania during the first Aveek in May, and arrive in Massachus- 

 etts about thj same time. 



PINE \vakbli:k. 



I>eii<h-ok'u vigoi'sii. 



Phitc \', Fig. I, male; Fig. "2, female. 



Size, 5.43 to 5.70. Greenish above; greenish-yellow be- 

 neath, obscurely streaked on the sides of breast with dusky 

 Wing bars, white. Common in Massachusetts in summer. 



