NELSON'S SHRIKE 179 



insects injured during the night. A shrike while killing prey is likely 

 to be practically oblivious to surrounding dangers, and its powers to 

 spring rapidly into the air are relatively poor. 



A shrike at Firebaugh, Calif., after retiring to its roost was heard 

 to give repeated frantic screeches when a horned owl perched on a i)ole 

 nearby. A barn owl, which approached and perched near the roost 

 shortly after the horned owd had left, provoked no such outburst from 

 the shrike. E. L, Sumner, Jr., has found the remains of shrikes in 

 horned-owl nests. Captive birds are greatly disturbed on being con- 

 fronted with dead hawks or owls. Similar fear is displayed when 

 hawks, cats, or dogs come near them. Therefore, there is some evi- 

 dence to indicate that shrike populations experience losses through 

 the feeding activities of large predatory birds and mammals. 



The known parasites of shrikes rarely produce death and cannot be 

 considered as contributing importantly to the death rate. 



Despite our ignorance concerning the causes of death in shrikes, the 

 life expectation of individuals can be estimated by indirect means. 

 Usually in Lanlus ludovicianus first-year birds make up about 50 per- 

 cent of winter populations. This means that annually half of the 

 breeding population of the preceding season die and are replaced by 

 first-year birds. If we assume that a family group in the spring con- 

 sists of tw^o adults and six juveniles, the succeeding year Avould, on the 

 average, result in the death of one of these adults and five of the juve- 

 niles. Most of the juveniles would be lost before leaving their parents 

 or during the first summer and autumn. Therefore, the juvenal and 

 immature death rates are high, and the average life expectation of 

 young upon leaving the nest is only about four months. The group of 

 immatures that successfully passes the first winter, later, as breeding- 

 birds, constitutes 50 percent of the total breeding population. Theo- 

 retically, during each succeeding year this same group must undergo 

 a 50 percent annual reduction by death. 



LANIUS LUDOVICIANUS NELSONI Oberholser 



NELSON'S SHRIKE 



HABITS 



The shrikes of this species living in the southern two-thirds of the 

 peninsula of Lower California have been separated by Dr. Oberholser 

 (1918) under the above name. He describes the form as "similar to 

 Laniiis ludovicianus gmnbeli^ but bill larger ; wdiite terminal areas on 

 outer rectrices much smaller; upper parts averaging darker, though 

 with the upper tail-coverts more conspicuously whitish; lower surface 

 more tinged with grayish, particularly on the posterior portion." He 

 gives as its distribution : "The southern two-thirds of Lower Califor- 

 nia, including the adjacent islands, north to 29°30" north latitude." 



