PART II. 
INTRODUCTION. 
OrniTHOLOGISTS of the present day are much indebted to 
the earnest and enthusiastic men who studied the habits 
of our birds in years past ; but truthful and careful though 
they may have been, being but men, they were fallible. As 
this is an age of advancement, it behooves us of the present 
day, while we are in a measure guided by these teachings, 
not to be biased by their conclusions, that we may detect 
the errors which they unconsciously committed. 
If, while endeavoring to correct some deeply seated error 
of the past, we disagree with our brother ornithologists, 
let us, with the spirit of the true naturalist, who would 
advance the study of Natural History, bring infallible proofs 
of its being an error, thereby convincing without offending. 
If in the following pages I unwittingly make mistakes, 
T am ready to be convinced by sufficient proof. 
In separating birds into species, too much dependence 
has been placed upon exceedingly variable characters as 
valid specific distinctions. For instance, the bill, although 
in the main retaining its shape, is sometimes subject to 
wide differences; this is well illustrated in the Terns, 
where they are extremely changeable in the length aud 
curve of the culmen; they also vary in coloration; yet 
in determining species, these points are now, and always 
have been, considered of value. 
The comparative length of the quills is another very 
