232 BULLETIN 113, UNITED STATES NATIONAL MUSEUM. 



6 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 30 

 yards from shore. On the date mentioned (May 24) 15 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 muskrat houses. The 

 majority of these nests contained three eggs, but a few of them held only one 

 and two, and one nest contained five. 



The habit of nesting on old and partially dilapidated muskrat 

 houses seems to be common at many places throughout the lakes and 

 swamps of the interior. In such situations little, if any, nest is 

 built, and sometimes two, or even three, sets of eggs are found on one 

 house. Usually the nest consists merely of a hollow excavated in the 

 half-decayed vegetable rubbish, but sometimes a few reeds, rushes, 

 or bits of grass, brought from a distance, are added to line the cavity 

 or build up a slight rim around it. 



Mr. Milton S. Ray (1903) describes a breeding colony of this 

 species in Lake Valley, California, in which — 



the nests were built in various situations. The majority were built up of dry 

 tules where the water is about 5 feet deep. When freshly built of green tules 

 the nest formed a pretty picture. They were placed among tall, thick tules or 

 marsh grass and pond lilies at their edge. Great difference existed in the nests, 

 some being elaborate structures, while others were scantily made and placed 

 on soggy masses of dead tules or floating logs. 



In Washington, according to Dawson (1909), these terns make use 

 of the old nests of the western grebe and sometimes even appropriate 

 an occupied nest of the latter. He shows a photograph of such an 

 occupied nest, and says he has " seen others in which the eggs of the 

 rightful owner were nearly buried under a little turret of dried 

 reeds, upon which the tern had been allowed to place her full com- 

 plement of eggs." 



Eggs. — In spite of the fact that the breeding season is much pro- 

 longed, and that early and late sets of eggs are often found, the 

 Forster's tern doubtless raises only one brood in a season. The nor- 

 mal set consists of three eggs, sometimes only two ; sets of four eggs 

 are common, sets of five are not rare, and even sets of six have been 

 reported. These larger sets usually, if not always, show evidences of 

 having been laid by more than one female, either in the shape, color, 

 or extent of incubation in the eggs. 



The eggs of Forster's tern are practically indistinguishable from 

 those of the common tern. In shape they are ovate, short ovate, or 

 elongate ovate. The shell is thin, smooth, and without luster. The 

 ground color varies from ' tawny olive " or " cinnamon buff " to 

 " cartridge buff " or " pale olive buff." The markings are usually 

 rather small spots, more or less evenly distributed, but often these 

 are congregated to form a ring on or near the larger end ; many 

 eggs are boldly and handsomely marked with large blotches or ir- 



