X PREFACE. 



ably other causes, as climatic, have been operating to effect 

 a gradual northward migration, in certain species at least. 

 These changes are of great interest, not only generally, but in 

 a scientific point of view, and we shall be able to trace them 

 and their causes only by comparing, from time to time, ex- 

 haustive faunal records of the same localities. 



"In a district so little diversified as that portion of Massa- 

 chusetts lying east of the Connecticut River, it is perhaps a 

 little unexpected that marked discrepancies should occur in 

 the observations made at adjoining localities by equally compe- 

 tent naturalists, in respect to the relative abundance of certain 

 species. As every experienced observer must have noticed 

 that the birds of passage, as many of the Warblers especially, 

 vary greatly in numbers in different years, and in the time 

 occupied by them in passing a given locality, it is less surpris- 

 ing .that at different points they should vary in abundance the 

 same year. Among the birds that regularly breed in the dis- 

 trict in question, there are some that -are not equally common 

 .at all points." 



"Birds, as probably other animals, are not quite so invari- 

 able in their habits as has been commonly supposed, nor in the 

 precise character of their notes and songs, or the situation and 

 materials of which they compose their nests. Hence one should 

 not rashly question the accounts given by usually reliable au- 

 thorities, because in particular instances they do not accord 

 with their own observations. Neither should differences in 

 habits, in song, etc., be taken as infallible evidence of a differ- 

 ence of species." 



"How universally the Chipping Sparrow (Spizella socialis) 

 breeds in trees, and generally at an elevation of several feet, 

 is well known, but several authentic instances of this bird's 

 nesting on the ground have 'corne to my knowledge, one of 

 which I myself discovered. Variations of this character in 

 other species are of occasional occurrence, examples of which 

 have doubtless been met with by every experienced collector. 



"The materials which birds select in the construction of 

 their nests are well known to vary in different localities ; the 



