Further Remarks on the Relationships of the Grackles of the Subgenus Quiscalus

Abstract

In the 'Bulletin of the American Museum of Natural History' for 1892 (Vol. IV, pp 1-20) I published a Preliminary Study of the relationships of the Bronzed, Purple and Florida Grackles. It showed that the Bronzed Grackle breeds from the Rio Grande Valley west to the Rocky Mountains, north to Great Slave Lake and Newfoundland, east to Connecticut and the Alleghanies; that the Florida Grackle ranged from Florida north to South Carolina and west to Louisiana, while the Purple Grackle occupied the area intervening between the ranges of the Bronzed and Florida birds. It was also shown that throughout its vast range, the Bronzed Grackle varied significantly in color only when it came in contact with the Purple Grackle with which it then completely intergraded. This intergradation was proven, by breeding specimens, to occur from Massachusetts to Pennsylvania but it was believed that it would take place wherever the breeding ranges of the two birds came together. The Florida Grackle, at least in peninsular Florida and north to Charleston, was shown also to be constant in color but the Purple Grackle was found to be so variable that it was described under three phases of color, (1) the bottle-green, (2) the bronze purple, (3) the brassy bluish-green. In my original paper I expressed a belief that the Bronzed Grackle is a species which intergrades with the Purple Grackle by hybridization, the hybrid being phase No. 3 of the latter; while the Florida Grackle was considered the highest development of phase No. 1 of the Purple Grackle. Further studies confirm my belief in the specific standing of a-neus and of its hybridization with the Purple Grackle, which I now find is accomplished in Louisiana, just as it is in the northern states, through phase No. 3 of the Purple Grackle. But instead of considering the Florida Grackle an offshoot of the Purple Grackle, I now take the opposite view and believe that the Florida bird is the ancestral form. This view is the logical outcome of a theory which introduces the climatic influences exerted by the last Glacial Period as fundamental factors in creating the conditions we observe to-day. It seems clear that, in order to hybridize, the ranges of the forms concerned must come together, and it seems equally clear that, in order to come together, they must previously have been apart. Whether, as my colleague Mr. J. T. Zimmer suggests, the ranges of the Bronzed and Purple Grackles may have been continuous prior to the last Glacial Period, there is certainly ground for the theory that during the height of this Period their ranges were disconnected. To the climatic influences of this time Dr. J. A. Allen was