180 bULLBTIN 191, UNITUD SlA'lliS NATIONAL MUSEUM 



animal activity, and of moisture on the ground may drive away these 

 birds, as soon as they are free of nesting duties, along with other species 

 that disappear at about the same time. The exodus may last only until 

 the shortening of the days reduces the evaporation and brings better 

 conditions. Movement toward the coast of only a few miles would 

 bring the birds to cooler and moister places. 



Tlie annual departure of the magpies, however, may reflect merely 

 physiological change in the birds independent of the conditions in their 

 habitat at this season. After the young are released from parental 

 care, there may be no attraction in one spot of ground to hold any of 

 the birds — nodiing to keep them from wandering freely. But after 

 a rest of a few weeks, faint beginnings of a new reproductive cycle 

 may require a definite home area, and thus the birds come back to begin 

 anew the cycle they have so recently completed. 



No doubt a nucleus of the returning birds consists of individuals that 

 left the same place, but the recorded observations indicate that a dif- 

 ferent number and presumably a slightly different set of individuals 

 return. Some of the recently hatched birds may stay in new spots; 

 they may join with other wandering groups and go to their home sites ; 

 they may come bac.k with the parent colony. Thus the returning num- 

 ber may be smaller or larger than the colony at the end of the nesting, 

 but it is rarely of the same size. The stabilization of numbers may 

 require several months, and always it extends over a much longer period 

 than the actual absence of the species from the area. 



Thus may be seen, in a species ordinarily considered as strictly resi- 

 dent, behavior that appears exactly like that of migratory kinds which 

 leave for long periods and which travel long distances. Once more it 

 appears that migration is a characteristic of all birds and may be exhib- 

 ited only in lesser or greater degree. It is not necessarily a basis for 

 sharply limited classifications of species. 



Voice. — Special attention to study of the voice of the yellow-billed 

 magpie led Richard Hunt to conclude that in fall the birds had only 

 one type of utterance, which, iiowever, was varied. (See Linsdale, 

 1937.) The three variations or phases listed here he considered distinct 

 enough to be described separately. His statements have been verified in 

 field observations by me. The three phases are as follows : 



1. Qtia-qua, qua-qua-qua, etc., given in series from two to six quas. 



The utterance is usually quite rapid when the qua'^ are more nu- 

 merous. The note is loud and the expression is rather good natured or 

 well disposed. The timber is raucous. It has more than a slight re- 

 semblance to that of the California woodpecker's "cracker" notes. When 

 birds of the two species are heard calling at the same time, the timber 



