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 122 THE CONDOR Vol. XIII breeders.* Definite i.nformation on the subject, covering the plains region east of the foothills, was practically a negligible quantity. The general impression con- veyed by text-books was that the extreme southern limit of the breeding range of most of the ducks lay far to the north of Colorado. Cooke in his final supplement of "Birds of Colorado" gave the first published intimation that this range might eventually be extended far to the south, and our work in this section verified the intimation. The results of systematic work brought to light many interesting and confusing facts, for we not only encountered many new peculiarities in nesting habits, but were also fortunate enough to collect data which established two species as breeders, whose status had heretofore been undetermined. A few species, e.g., the Mallard, Blue-winged and Cinnamon Teal, Baldpate, $hoveller, Gadwall and Ruddy Duck had already been definitely established as breeders on the plains. Of these we found the two species of teal nesting commonly, in fact the Blue-wings might be Fig. 37. NESTING SITE OF MALLARD ON MUSK-RAT HOUSE considered abundant breeders; the Ruddy a rather uncommon breeder; persistent searching netted us only two nests of the Mallard and one of the Shoveller, al- though the birds were present in considerable numbers throughout the nesting season; and the most careful field work failed to reveal a single nest of the Bald- pate or Gadwall, although these birds were also fairly common. The Green- winged Teal was seen in some numbers, but we found only one nest which we could assign positively to this species. One of our most interesting discoveries was that the Pintail, which had hither- to been considered a rather rare breeder in the state, was, next to the Blue-winged Teal, the most common breeding duck in the Barr Lake country. The most important result of our work, however, was in establishing the Red- head and the Canvasback among Colorado breeding birds. In order to prevent re- petition it will no doubt be advisable to arrange the data according to species, rather than to treat the various ducks indiscriminately. In the following notes
 * All the notes upon which this paper'is based were taken in company with L. J. Hersey.