458 University of California Publications in Zoology [Vol. 11 



Whether butterflies are too active to be caught, or whether they 

 are unpalatable because of odor or taste, are questions still await- 

 ing an answer. In any case it can truly be said that butterflies, 

 considering their abundance, are not taken as food in anywhere 

 near the proportion that other insects are taken. That four of 

 the larger common birds of the region should have fed upon these 

 insects and that one of these should have fed almost entirely upon 

 them is certainly significant. 



It cannot be said that lack of other food caused these birds 

 to turn their attention to butterflies, for many of the birds col- 

 lected had either taken no butterflies or but one or two. The 

 butterflies were not only conspicuous, but extremely abundant. 

 Some idea of their numbers can be obtained when it is known 

 that in damp places or along the banks of streams, where the 

 butterflies had gathered to drink, as many as one hundred and 

 fifty individuals were counted in one square foot. In order to 

 estimate the numbers flying counts were made of the individuals 

 passing between two fir trees about tweuty feet high and standing 

 about thirty feet apart. The counts for ten successive minutes 

 between 4:40 and 4:50 p.m. on Augu.st 20, 1911, were as follows: 



1st minute 10.5 7th minute 96 



2nd minute 119 8tli minute 102 



3rd minute 130 f<th minute 83 



4th minute 102 10th minute 112 



5th minute 134 



6th minute 100 Av. per minute .. 108 



It can readily be seen, therefore, that butterflies were the 

 insects most available at the time. The significant thing is that 

 certain birds changed their food habits to meet the changed con- 

 ditions. Birds collected in the same locality before the butter- 

 flies became abundant had taken no butterflies. 



The investigation did not show that birds can be depended 

 upon to control butterfly outbreaks, for the numbers taken com- 

 pared with the actual numbers of the insects were insignificant. 

 The fact that the birds attacked the insect at a critical time in 

 its life-history — the adult stage when the death rate is at its 

 minimum and the insect has the best chance of surviving till egg- 

 laying — made the work of birds more important than if they 



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