NORTHERN SHRIKE 125 



(ered was the man with the gun on Boston Common, who killed over 

 50 of the birds in a single winter, many years ago, to protect the 

 English sparrows soon after their importation. The tables are turned 

 now, for one of the best things the shrike does is to help reduce the 

 numbers of this ubiquitous foreigner, so the shrikes are now welcomed 

 in the cities. 



Harold S. Peters (1930) lists only one louse, Ph'dopterus sui- 

 fiavescens, as an esternal parasite on the northern shrike. 



Whiter. — The northern shrike comes southward to spend the winter 

 in varying numbers at more or less regular intervals, depending prob- 

 ably on the variations in its food supply in its summer home. Some- 

 times it is abundant in New England in winter, sometimes rare, and 

 sometimes entirely absent or very local. They were reported as very 

 abundant in the winter of 1878-79. Mr. Floyd (1928) called atten- 

 tion to a decided invasion in the winter of 102G-27, in Maine, New 

 Hampshire, Vermont, Massachusetts, Rhode Island, Connecticut, 

 New York, and New Jersey, and they were unusually plentiful in 

 Nova Scotia. He corresponded with bird-banders from New England 

 to Virginia and learned that "during the six months from October to 

 April, sixty-two Shrikes were reported destroyed by banders, while 

 eight were banded and released." He attempted to learn whether the 

 abundance of shrikes coincided with the heavy invasions of redpolls, 

 siskins, and other small northern birds, on which the shrike might 

 prey, but the data accmnulated did not confirm this theory; in fact, 

 there was only one year out of eight in which the small birds and 

 shrikes were both abundant. 



David E. Davis (1937) has made a study of this subject and says 

 in his interesting paper on it : 



The Northern Shrike {Lanius doreaUs lorealis) has attracted attention by 

 its occurrence in New England and adjoining States, in large numbers in certain 

 years. Since the species is predatory, a correlation with the well-known cycle of 

 mice (Microtus spp., Dicrostonyx spp.) was suspected. * * * ^ thorough 

 examination of the available literature was made for records concerning shrike 

 invasions. It was soon apparent that the Christmas Bird Census in "Bird-Lore" 

 supplied the only data which could be used to compare one year with another. 

 These records are here presented in a graph showing the number of birds 

 observed per census for each Christmas period. * * * That there is a defi- 

 nite cycle is at once apparent from the graph. The average is 4.2 years. It 

 should be noted that there are two five-year periods and no three-year periods. 

 The winters of maximum abundance are 1900-01; 1905-00; 1909-10; 191.3-14; 

 1917-18 ; 1921-22 ; 192G-27 ; 19;]0-31 ; 1934-85. That there was a maximum in the 

 winter of 1900-01 is supported by Brewster (190G) who states that shrikes were 

 not seen in 1902, 1903, or 1904, but were rather common in 1901. * * * it 

 is quite obvious that the mice increase and periodically die out. During the 

 increase of mice, the predators likewise increase. * * * When the mice 

 disappear the predators first exhaust other prey and then either migrate or 

 die. 



