84 Trans. Acad. Sci. of St. Louis 
Evanston averaged 2.19 em. by 1.50 em. The thirteen eggs of 
four sets at Ithaca averaged 2.28 em. by 1.59 em. Whether there 
is any significance in this discrepancy I cannot say. Though 
Ithaca eggs were larger, on the other hand, Evanston nests 
were larger. Probably both discrepancies would disappear. in a 
large series. 
The actions of the adult birds during egg laying have already 
been discussed under nest-finding. More need not be said here 
except that the actions of the female at this period are those of 
a bird with an infinity of leisure, patience and unconcern. She 
does nothing but remain quietly in one place, forever preening 
herself. The male at this time, attends her as assiduously as a 
groom. Now frequently incubation begins before the set is 
complete but the actions of the female then constitute another 
matter. 
Incubation period.—Forbush (1927) gives the following pe- 
riods of incubation: 12 days (H. O. Green) ; 11 days (L. Mel. 
Terrill) ; 14 days (A. W. Butler). Jones (1892) puts the aver- 
age at 13 days and says, “I doubt if any eggs are hatched in less 
than 12 days.’’ As already has been noted no nest was fol- 
lowed from the time of the first egg to hatching, but in three 
instances the last egg was laid after the nest was found. This 
last egg, or the last young which was most probably of this egg; 
hatched on the 12th day after laying, in the three cases. From 
the time of laying to the time of hatching about eleven days 
would have intervened. The incubation period determined by 
MacDonald (1916), for O. a. leucolaema, was in exactly the 
above fashion; a fourth egg was laid after a nest with a set of 
three was discovered: All hatched within twenty-four hours of 
each other, eleven days from the laying of the last egg. Her 
conclusions that incubation extends from eleven to fourteen days 
is unwarranted, however, for it is at once obvious (since all 
hatched together), that incubation did not begin until the last 
egg was laid. At Evanston, however, the last to hatch was often 
a full day behind all the others in many of the early sets, that is, 
three would hatch within an hour or two of each other, the 
fourth almost exactly twenty-four hours later. No other con- 
clusion is logical but that incubation began the day before the 
last egg was laid (the nest was found because the bird had be- 
gun to incubate) and that eleven days is the period for all. 
