6 PACIFIC COAST AVIFAUNA No. 12 
this publication been content to state their findings in the text, without changing 
the formal headings under which these species are placed. This appeared to be 
the best plan, in the interests of convenience and uniformity. 
In the treatment of records objection may be made that some unconfirmed 
ones are included, while others, at first glance apparently just as trustworthy, 
are relegated to the hypothetical list. I have endeavored to act conservatively in 
this; but one need not be as strict in such matters in the case of a local paper as 
in a state list, and I have therefore accepted sight records, by competent observ- 
ers, of birds not too hard to identify in the field and belonging to such species as 
one might expect to find upon the islands. On the other hand, in the case of sin- 
gle, sight records, of birds that are especially hard to differentiate in life from 
closely allied forms, relegation to the hypothetical list has been the only course 
open to me. As regards another type of record: We know that Dr. J. G. Cooper 
was a most capable and scrupulous ornithologist; but in his time men did not 
keep as exact notes, nor label their specimens with as much eare, as they now do. 
I find that several of Cooper’s island skins were wrongly identified, while there 
seem to be a number of mistakes and inconsistencies in his published notes. 
Therefore, any unusual records of his, unless verified, have been placed in the 
hypothetical list. 
In the cases of birds that do not breed upon the islands, it is often difficult 
to judge as to their numbers and the regularity of their visits. Therefore, in- 
stead of merely citing a few winter records without any explanation, I have 
stated, when there are instances of the occurrences of a species upon more than 
one island, the probable numbers in which it’ is found, judging from its relative 
abundance on the nearby mainland and the apparent likelihood of its occurring 
regularly upon the islands. In general I have endeavored, besides giving man- 
ner of occurrence, to present any little-known habits that may be of interest, 
especially those relating to species or subspecies which are confined to the islands. 
Generally speaking, it is a bad plan in any science to advance fanciful theo- 
ries, impossible to prove; for a science should be built up of facts. With some 
things, however, as for example, with bird migration, it is impossible to make 
absolute statements as to cause and effect, and in such cases it seems justifiable 
to advance theories, which, even though eventually shown to be incorrect, do good 
by promoting further discussion. With such an idea IT have submitted several 
theories in the following chapter on ‘‘Problems presented by the island avi- 
fauna,’’ the resulting conclusions, though not considered as absolutely proven, 
having been reached through careful consideration of the known facts. While 
not submitted as final, I trust that they may prove of assistance in building up a 
further understanding of our insular bird life. 
