50 BULLETIN 107, UNITED STATES NATIONAL MUSEUM. 
Loons are reported by many observers as nesting on muskrat 
houses. I have never seen such a nest, but suppose they must select 
the old, abandoned houses or else build up piles of rubbish them- 
selves which look like muskrat houses. I believe that they prefer 
to occupy the same nest every year and they probably add to it a 
little each year. 
Eggs.—This loon lays normally two eggs, one of which is often 
infertile; sometimes only one egg is laid and occasionally three are 
found in a nest. Audubon was quite confident that three eggs was 
the usual number and many other writers have referred to it. I 
have never found a set of three eggs and believe that they are very 
rarely seen. The eggs vary but little in shape from “elliptical 
ovate” to “elongate ovate.” The shell is thick, smoothly granular, 
and has a dull luster. The ground color varies from dark to light 
olive brown or from dark to light olive green with various inter- 
mediate shades. They are rather sparingly marked with small spots 
of “clove brown” or “bister,” and occasionally with lighter spots of 
drab; the markings are usually much scattered. I have seen it stated 
in print that a set usually contains one brown and one green egg, 
but I have not found it to be so in the nests that I have examined. 
The measurements of 41 eggs in various collections average 88.9 by 
56.2 millimeters; the eggs showing the four extremes measure 96.5 
by 61 and 82 by 52 millimeters. 
Only one brood is raised in a season, but if the first set of eggs is 
taken, another set is laid within three or four weeks; sometimes even 
a third set is laid if the first two have been disturbed, but this would 
not be likely to happen unless the first set was laid very early. Mr. 
Ora W. Knight (1918) gives the period of incubation as “ very close to 
29 days.” The pair keep together during the incubating period and 
probably both take part in it, though this is difficult to determine, 
as the sexes look so much alike. Incubation is practically continu- 
ous; the eggs are never allowed to become too cool, though they will 
stand considerable chilling, and they are never covered with rub- 
bish. While incubating, the loon sits very low and is spread out 
quite flat; she is not so conspicuous as her striking colors would 
indicate. 
Young.—Mr. C. William Beebe (1907) made a study of two young 
loons, which were hatched from eggs brought to the New York Zool- 
ogical Park, from which he drew the following conclusions: 
It is probable that young loons are, from the first, fed on whole, not on 
macerated or regurgitated fish. The actions of swimming and preening are 
instinctive. The method of swimming is usually by alternate strokes. These 
become simultaneous when a sudden spurt or great speed is desired. The arc 
of the swimming stroke, in the young chick, is much more lateral than in the 
adult bird. Loon chicks can progress more easily and rapidly over the ground 
