50 BULLETIN 107, UNITED STATES NATIONAL MUSEUM. 



Loons are reported by many observers as nesting on miiskrat 

 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 cgss, one of which is often 

 infertile; sometimes only one ^gg 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 ^gg., 

 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 83 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. 0. 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 



