As initially projected, this report would have been considerably larger. Fuller discussion of the systematics of many species would have been desirable and the inclusion of life-history observations and allied subjects would have added considerably to its usefulness. In normal times this would·have been possible, for investigation to fill in the not inconsiderable gaps was definitely on schedule for. 1942 and 1943. During the enforced postponement of such plans the outlook has been altered some- what and activity for the post war years has been greatly enlarged- in prospect. Indeed, preliminary field work and systematic studies on the larger project have already been initiated and a major part of the bibliography (additional to that incorporated here) has been compiled.
Publication of a distributional paper on the birds of Sonora is justifiable on several grounds, the principal one of which (from a personal standpoint) is the hope of stimulating interest and activity in Mexican. ornithology, particularly in regions adjacent to our southern boundary and most particularly in the area of the Gulf of California. This last is a great region of extremely high speciation potency, a natural laboratory the importance of which from a general biological viewpoint is not yet fully comprehended. In it there are innumerable fields for investigation~ limited or extensive according to will and ability. Even the ornithology of the peninsula of Baja California, so intensively, and as it seemed at the time so exhaustively, treated by Grinnell in 1928, is in need of review. I refer not alone to the purely systematic aspect, but also to the more comprehensive question of the origin of the avifauna. .This has been presumed, justifiably on the then existing evidence, to be almost wholly of northern derivation. But now I, at least, am not sure but that in many instances a cross-Gulf relationship does not provide the better answer. In a few instances this can be well demonstrated, in others it is strongly- indicated, and in still others suspected. Many more data must be in hand, though, before reasonably certain conclusions can ·be advanced for consideration. Similarly, some current conceptions of relationships of parts of the Sonora avifauna doubtless will undergo revision as time and further exploration in the Gulf area dictate. Meanwhile, it is to be hoped that the present distributional synopsis will, by its very incompleteness,. provide a stimulus for new work.
AJ Van Rossem
University of California, Los Angeles March 22, 1945