26 BULLETIN 17 0, UNITED STATES NATIONAL MUSEUM 



Weights taken at nest number 1, when adjusted to compensate for age, and for 

 full or empty crop, correspond closely with the longer and more complete record 

 taken at nest number 2, and are therefore not here included. 



* * * This pair [nest no. 2] were mighty hunters, remarkable for the variety 

 of their quarry. They also had the habit of bringing in their game intact to the 

 nest, or to a small shelf near the base of the cliff, and there plucking the birds and 

 leaving the remains, after satisfying the ravenous family and their own appetites. 



This habit is rare, I believe. Usually the mammals are torn into and partly 

 eaten before being brought to the nest to feed to the young. When the feeding 

 is about completed, the parent lifts the remains in its beak, makes a running start, 

 and on the instant of taking wing shifts the remains to its talons. On some rocky 

 point in the vicinity it then probably cleans off and eats the scraps of meat from 

 the skin and bones, and leaves them where they are never found for record. The 

 larger birds are ordinarily partially plucked before being brought to the nest, and 

 the fag ends are probably carried away at the end of the feast. Smaller birds 

 disappear on the spot as if by magic. This habit of carrying remains away was 

 observed from the blind in 1930 * * *. 



It is difficult or impossible to estimate definitely the number of animals repre- 

 sented by a given numbers of pellets from a nest. All the young may receive a 

 full crop of fur from a single large ground squirrel. In a family of five, such as 

 that at nest number 1, this meal might result in five pellets available for analysis 

 from the death of one animal. On the other hand, five pellets found at the roost- 

 ing place of a mature bird would almost certainly have meant at least five animals 

 killed. * * * 



After the photograph and movie campaign of 1930 had been completed, four 

 pellets were found on the edge of the mesa, just behind the old bird's lookout rock 

 across the canon; none was found at the base of the rock. These pellets measured 

 2.00x 0.80 in.; 2.12 x 0.88 in.; 1.82 x 0.90 in.; and 2.10 x 0.90 in.; they are nota- 

 bly more compact and symmetrical than those of the young. 



Observation of falcons in captivity coupled with the fact that these wild birds 

 deserted their lookout point for the firmer footing of the flat mesa shows that the 

 process of casting up a pellet is a serious and sea-sick business. When the symp- 

 toms of "casting" first attack a falcon it draws its feathers down flat, stands up 

 full height, sticks its head and neck outward and upward, and for a few moments 

 looks bereft of its senses. It then starts to duck its head in a series of quick jerks, 

 at the same time contorting its neck violently from side to side. This muscular 

 action appears to force the relatively large pellet from the bird's interior upward 

 into the crop. The sidewise contortions then cease, and the pellet is cast by a 

 series of up and down pumpings of the head and neck. The bird then stands for 

 a few moments seemingly with the sad question in its mind — "Would a good dose 

 of Mothersills have obviated all of this?" It then shakes itself, resumes its 

 interest in life, and begins to wonder where the next supply of fur and feathers is 

 available. * * * 



Probably a definite weight of meat (with comparatively little variation one way 

 or the other) is required to develop a young falcon from the egg to the day of 

 flight. Whether this food supply consists of tender birds or tougher rodents 

 probably makes little difference in the total weight consumed. However, toward 

 the end of the nest life the demands of the family are so tremendous that an end- 

 less stream of mammals and fair sized birds seems to be the only recourse of the 

 hard-working parents. Small birds could hardly be caught fast enough. 



The food actually secured probably depends to a large extent on the locality, 

 the season, and the individual hunting ability of the parents. In the general 

 locality of these studies ground squirrels and meadowlarks (being the most 

 readily available source) probably form a large part of the normal supply of the 



