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 Mar. ,1911 NESTING OF THE FORSTER AND BLACK TERNS IN COLORADO 59 surface of the water (although in reality the nests were supported by masses of dead cat-tails beneath the surface of the water) and were very c6nspicuous owing to the lack of concealing vegetation. The eggs were deposited in the center of the pile in a neat depression, which was lined with small bits of the same material. The bottom of the cavity was, in every instance, well above the surface of the water (usually from two to six inches) and the nest cavities were entirely free from moisture. Most of these nests were built in comparatively open water almost waist deep, and about thirty yards from shore. On the date mentioned (May 24) fifteen nests were examined, about a third of which were constructed by the birds as described, while the remaining two-thirds were the usual depressions, in musk-rat houses. The majority of these nests con- tained three eggs,but a few of them held only one and two,and one nest contained five lig. 25. CLOSE VIEW OF FORSTER TERN'S NEST SHOWING DETAIL OF NEST CON- STRUCTION; NOTE THE TwO COLOR TYPES OF EGGS, THE TwO IN THE FOREGROUND BEING OF THE DARK BROWN TYPE AND THE THREE N BACrGROUND OF rIGHTER GROUND-COrOR This "set" together with all the other sets of five and six examined by us contained eggs of two very distinct types of coloration, one type having a decidedly greenish ground color with small spots and blotches of brown; the other type hav- ing a clear brownish or reddish brown ground color, with much larger spots and blotches of very dark brown; and it is altogether probable that the two color types were laid by different birds though in the same nest. In fact after careful observa- tion we came to the conclusion that three eggs composed the maximum set (with rare exceptions) and that nests containing five and six eggs were the depositories of more than one bird. We are at a loss to account for this peculiar feature, as we did not see more than one bird around any one of the nests, and unoccupied nest- ing sites were abundant upon every hand.