Mar., 1911 
XESTINCr (9E THE FORSTER AXD BLACK TERXLS IX 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 conspicuous 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 
Eig. 2,5. CLOSE VIEW OF FORSTER TERN'S NEST SHOWING DETAIL OF NEST CON- 
STRUCTION; NOTf; the TWO color types OF EGGS, THE TWO IN THE 
FOREGROUND BEING OF THE DARK BROWN TYPE AND THE THREE 
IN BACKGROUND OF LIGHTER GROUND-COLOR 
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 browm; 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. 
