480 



THE NATIONAL GEOGRAPHIC MAGAZINE 



Photo from Stanley K- Piper, U. S. Biological Survey 

 ALFALFA PLANT KILLED BY MICE 



smaller seed-eating birds suffered ex- 

 tremely. On one occasion 67 horned 

 larks were found dead on about 4 acres 

 a few hours after the poisoned grain had 

 been distributed. Fortunately hawks 

 owls, gulls, and ravens were not affected, 

 but many skunks and domestic cats were 

 killed as the result of eating mice dying 

 or dead of phosphorus. Several acci- 

 dents occurred in handling the solution, 

 and cases of fatal poisoning of live stock 

 were frequent. 



Several attempts by ranchmen to in- 

 duce contagious diseases among the mice 

 by means of advertised bacterial prepara- 

 tions failed. 



ASSISTANCE) OP THE) U. S. BIOLOGI- 

 CAL SURVEY requested 



Chiefly through the coopera- 

 tion of Mr George S. Webb, 

 manager of the large Rodgers 

 ranch, systematic experiments to 

 destroy the pests, undertaken 

 early in January, 1908, by the 

 Biological Survey, demonstrated 

 that such mouse plagues can be 

 controlled and the greater part 

 of the losses prevented. The ex- 

 periments of the Survey proved 

 that mice can be effectively de- 

 stroyed in winter by alfalfa hay 

 poisoned with strychnia sulphate, 

 and this preparation was gene- 

 rally recommended in the valley. 

 On the Rodgers and Anker 

 ranches a force of 7 to 15 men 

 was employed to distribute the 

 poison in the fields, with most 

 satisfactory results, and without 

 the dangers incident to the use 

 of phosphorus and grain. 



By March 15 poisoning, sup- 

 plemented by natural agencies, 

 had destroyed the mice on sev- 

 eral thousands of acres where 

 they were most abundant, and 

 the plague was broken before the 

 remaining alfalfa fields had been 

 overrun. In scattered centers 

 mice continued in destructive 

 numbers until May, but without 

 regaining to any considerable ex- 

 tent by reproduction they steadily 

 decreased. Later in the summer they 

 had almost disappeared from the valley. 



$300,000 DESTROYED BY THE MICE 



The scourge of mice had swept over 

 about four-fifths of the cultivated area 

 in the lower part of Humboldt Valley. 

 Of 20,000 acres in alfalfa, about 15,000 

 were so seriously injured as to require 

 plowing and replanting. Over most of 

 this area the alfalfa was replaced by 

 grain crops for the season of 1908 at 

 great expense and loss, since good alfalfa 

 lands pay gross returns of from $60 to 

 $70 per acre, while good grain crops re- 

 turn only $35 or $40 per acre. 



