PRAIRIE FALCON 27 



average falcon family. Here, and elsewhere, it is probably more difficult for the 

 parents to raise a brood hatched a month late than one hatched at the normal 

 time. The hunting ability of the parents is a prime factor in at least the variety 

 of the food supply. 



Only by observing a large number of families can a true estimate of the falcon's 

 economic status be established. 



Mr. Fowler (1931) also gives the following data in detailed tables: 

 At Nest no. 1 a partial tabulation showed that 1 California horned lark, 

 8 western meadowlarks, and 9 California ground squirrels were eaten 

 between April 29 and May 20, 1928. At Nest no. 2 it was possible to 

 make much fuller tabulations, showing 2 mourning doves, 8 burrowing 

 owls, 3 California horned larks, 9 California jays, 15 western meadow- 

 larks, 3 Brewer's blackbirds, 2 California shrikes, 1 rock wren, 1 

 poultry, 1 unidentified bird, 1 California pocket gopher, 7 California 

 ground squirrels, and 1 Nelson spermophile eaten by four young 

 between May 6 and June 6, 1928. The poultry item was "one small 

 white wing about the size and shape of a meadowlark; probably a 

 Leghorn chick from a neighboring ranch", but a detached wing might 

 have been picked up so far as data show. 



Speaking of a nest in Montana, Cameron (1907) says that a pair of 

 Say's phoebes that built a nest "in a hole near the Prairie Falcons' 

 eyrie were killed by the latter for their young." 



Plumages. — Falconets just out of the egg, or at least as soon as 

 they are dry, are covered with fine white down. When the birds are 

 about two weeks old the darker feathers of the tail and wings become 

 noticeable, and a few days later various feather tracts on the body 

 outline themselves. At about four weeks of age, the feathers are 

 well started. During the following week the feathers grow so fast 

 that the bird actually loses some of its body weight, although ample 

 food may be greedily swallowed. The changes in color are rapid, 

 so that a young bird five or six weeks old is really darker above than 

 the adults. Although this coloration is rich, it is still obscured 

 until the shedding of the last down at some two months of age. The 

 final growth of plumage and the last shedding of down take 

 place after the young are on the wing. The young falcons out of the 

 nest are buffier and more striped than the adults, with a more red- 

 dish tinge to the upper parts; the iris is brown; the feet and legs are 

 slate color; the claws, black; the bill, bluish black, with the base of the 

 under mandible yellow. It is not known just when the changes are 

 completed, but gradually the juvenile plumage becomes lighter, 

 clearer, and more like the adult. The feet and legs become yellow, 

 while the mandibles and iris change little, if any. Bailey and Niedrach 

 (1933) write: 



Out came the female falcon. And, what a bird! Niedrach had promised a 

 surprise, but such a beautiful hawk was not expected. Instead of the natural 

 brown plumage of the species, this bird was cream white, with occasional markings 



