178 BULLETIN 197, UNITED STATES NATIONAL MUSEUM 



song that has led observers to claim that shrikes imitate other birds. 

 However, I have consistently failed to detect anything in these songs 

 that could definitely be called imitation. Captive juveniles that never 

 had heard songs of other birds or of shrikes uttered primitive songs 

 identical with those given by wild shrikes. Such songs of cage birds 

 are purely instinctive and unlearned. 



The screech or call note consists of 4 to 10 or more harsh forceful 

 utterances of diminishing intensity, the first notes slightly higher 

 pitched and shorter than the terminal notes, although pitch is difficult 

 to detect in a sound so thoroughly discordant. A metallic variation 

 of this call note occurs during nuptial displays. 



Single notes, schgra-a-a^ of a quality less sharp than that of the 

 screeches, variously repeated and resembling the huskier notes of 

 Cyanocitta stellein, are given by birds while defending their nests. 

 These notes are each longer in duration than a single screech of the 

 call-note series. This type of note also may be given while a logger- 

 head shrike is worrying prey it cannot readily kill. 



Staccato clucking notes are heard during attacks upon invaders or 

 when birds are in a defensive attitude. 



The pulsating or begging notes of young and the begging notes of 

 adults are extremely similar, although slight differences in quality may 

 be detected. The tsp and tcheep of young in the nest, fear notes of 

 juveniles, the juvenile's "location note," screig, and the nest call of the 

 parents have earlier been described. 



There is but one note given by cage birds that I have failed to hear in 

 the wild and have not seen mentioned in the literature. This is a low- 

 pitched chuckle of weak intensity, which cage birds give when ap- 

 proached and when completely at ease, that is to say, when they are not 

 frightened or in any way excited. 



Captive nestlings develop perfectly all the notes of wild shrikes with 

 the exception of the rhythmic types of song. 



Enemies. — Unfortunately little is known concerning causes of death 

 in California shrikes. These birds are moderately large, aggressive, 

 and well equipped to fight, and it is difficult to understand what hap- 

 pens to the relatively large number of young hatched annually. 



Instances of death other than by shooting I have noted have occurred 

 as a result of accident caused by automobiles on roadways. Robert- 

 son (1930) includes in his discussion of death of birds on roadways 

 records of ten California shrikes found dead during one year on the 

 roads bounding a region roughly 10 square miles in an area in southern 

 California under his daily observation. He concludes that the most 

 likely cause of death is collision with automobiles and that death is not 

 caused to any extent by collision with overhead wires or by shooting. 

 Birds probably are struck down by automobiles most commonly early 

 in the morning, for the road surfaces at that time are well baited with 



