depends largely on the fate of the early nests, so that a primary 

 objective of management should be to safeguard these attempts."* 



Decline in Size of Broods 



In 1950, when I was unable to be on the study area, Mr. William 

 Brecheisen, Jr. recorded all broods seen in the course of his normal 

 farming operations. He did not estimate ages of the chicks after 

 they were half grown, and the data that he gathered can best be 

 treated according to the date of observation. The results of his ob- 

 servations, presented in Figure 7, reveal that broods ranged in size 

 from three to fifteen, averaged approximately eight chicks at the 

 beginning of the season and averaged 6.6 at the end of the season 

 in August. 



15 



a 

 O 

 O 



ec 10 



CO 



Z 



CO 



z 



10 

 MAY 



20 



30 



9 



JUNE 



Id 



29 



9 

 JULY 



19 



29 



8 

 AUG. 



DATE OF OBSERVATION 



Fig. 7. Scatter diagram of size of brood seen (Y axis) plotted 

 against the date of observation (X axis) and the regression line of 

 Y on X. r = —.191. Data from the Welda Area, 1950. 



In 1951, the flushing device previously described was used to 

 find broods in pastures; and early morning work with a dog located 

 broods in cultivated land where the flushing device could not be 

 used. Six hundred and twenty acres of the study area, plus eighty 

 acres outside the area, were censused. A total of eighteen broods 

 able to fly were found ranging in number of individuals per brood 

 from two to twelve. Figure 8 presents the distribution and decline 

 in size of these broods. The average number of individuals per 

 brood was four and one-half as compared with approximately seven 

 in 1950. The decline in number of individuals per brood, after the 

 young were able to fly, was less than in 1950, r = — .091 in 1951 as 

 compared to r = — .191 in 1950. Another difference between the two 

 seasons was that the first broods were seen 19 days earlier in 1950. 



If it is true that breeding activity is controlled by a combination 

 of light and temperature (see Hamerstrom, 1939:108), then a com- 



[29] 



