PRAIRIE FALCON 25 



again and again. The last time, the motion-picture camera was 

 started as she approached, "and in a few moments she alighted as 

 before. Motionless, with wings dropped, she looked at the blind, 

 and finally, apparently satisfied that all was well in spite of the whir- 

 ring noise, settled down upon her eggs." On the following day two 

 downy young sprawled on the rocky shelf. The mother returned in 

 half an hour to cover the falconets and the other two eggs. 



When the young falcons first leave their eggs they are as helpless 

 and ill-formed as any birds could be. During the following five weeks 

 they are carefully looked after and fed by the female parent. They 

 grow rapidly, and at the end of this period they leave the nest and are 

 soon able to care for themselves. Taverner (1919a), however, dis- 

 tinctly noted that the young, after leaving the nest, "while full-fledged 

 and apparently strong on the wing, were under parental care." 



Although we have many accounts of finding the nests and of secur- 

 ing the eggs, with whatever habits could be noted at the time, only 

 one scientist, that I know of, has had the time and patience to make a 

 detailed study of the brooding, care, and growth of the young. F. H. 

 Fowler (1931) made this study in 1928 in the canyons of the eastern 

 side of the Mount Hamilton range of mountains in California. The 

 nest that he designates as Nest no. 1 on April 29 "was found to contain 

 five young falcons, about nine days old, according to subsequent 

 weight comparisons. [Full set of eggs was found April 1.] Nest 

 number 2, which could not be visited until May 6, then contained 

 four very young birds, believed, after much subsequent study and 

 figuring, to average about three days old. [Full set of five eggs was 

 found April 1.]" Mr. Fowler continues: 



They were weak, had a marked tendency to capsize, and when they did roll over 

 immediately curled up as if still in the shell. Only the most advanced had their 

 eyes part way open, and the others showed very marked and extensive granulation 

 around the unopened ej^elids. No remnants of the fifth egg, nor of a chick 

 hatched from it, could be found. 



The young in nest number 1 were systematically weighed and photographed in 

 the nest, until the family took to wing some time between May 23 and the next 

 visit on May 30. Those in nest number 2 were weighed, and a selected bird 

 photographed to scale, until they appeared ready to leave the nest when last 

 visited June 6. 



The weights of a typical young falcon are as follows (condensed 

 from Fowler's diagram): 



May 6,1928 3 days old weighed 2 }{ ounces 



May 13, 1928 10 days old weighed VA ounces 



May 20, 1928 17 days old weighed 14 ounces 



May 30, 1928 27 days old weighed 20 ounces 



June 3, 1928 31 days old weighed 19 ounces 



June 6, 1928 34 days old weighed 18 ounces 



13751—38 3 



