136 Trans. Acad. Sci. of St. Louis 
E. The nesting. 
1. Season of nesting. The literature contains four February 
records of nests and many records of March nests in many states, 
and two or three records of nests in July. The writer has records 
of nests from about March 21 to July 12, in 1926, at Evanston, 
Illinois; from about March 11 to June 28, 1927, at Ithaca, New 
York. 
2. Explanation of March nests. It is suggested that such a 
strange phenomenon as that of a Passerine bird nesting in March 
cannot be explained easily. The bird has too long a nesting 
season to explain it on the conditions that might exist in early 
spring alone; and then, in the range where the Prairie Horned 
Lark was studied, nests are frequently destroyed by inclement 
weather and many young die of starvation at this season. Since 
this bird demands barren conditions, and not verdure, for a nest 
site, the conditions are suitable very early and it is suggested 
the early-nesting physiological cycle may have been acquired in 
a more propitious climate and subsequently carried north and 
east. It is further noted that O. a. actia of —— nests in 
March where conditions are quite ideal. 
3. Weather control of March and April nests. With one excep- 
tion, all observed nests (a total of fourteen) of March and April 
were not begun until the mean temperature rose above 40 degrees 
Fahrenheit for two or more days in succession. The exception 
was the initiation of a nest on the first day that the temperature 
rose above a mean of 40 degrees Fahrenheit. Once weather con- 
ditions, suitable for the initiation of nesting activities, prevailed, 
no subsequent weather, no matter how severe, (excepting deep 
snow only) would inhibit these activities. Even birds that had 
nested in March and whose nests were destroyed by late March 
and early April snows, would not renest until weather condi- 
tions were as given, though this necessitated a delay of nearly 
three weeks in two cases at Ithaca, N. Y. That this was a delay 
eaused by the weather is easily demonstrated by the fact that 
an exceptional case (noted above) began renesting on a single 
suitable day, but two other Larks waited two weeks longer for 
renesting when weather again was suitable and for a longer 
period. (See Figure 8.) It is known that two of these birds, 
and probably all, had had former nests. 
On the basis of this known weather control it was possible to 
