PEOTEOTIVB COLOEATION". 91 



as a rule only seize their prey wlien moving; in tliese instances 

 a protective coloration would be no additional advantage ; it 

 would be simply superfluous. 



Tliese arguments do not, however, apply to birds, which 

 admittedly search for insects assiduously on the ground and 

 among trees. Insectivorous birds are mostly small and very 

 keen-sighted ; I have frequently observed that they will readily 

 detect the smallest insect or particle of food when thrown 

 amongst gravel ; and the observation is by no means new. 



Judging of birds by our own standard — which is the way in 

 which nearly all the problems relating to colour have been ap- 

 proached — does it seem likely that we should fail to see a cater- 

 pillar, perhaps as long or longer than the arm, of an obviously 

 diiBferent texture from the branches, and displaying in many cases 

 through its semi-transparent skin the pulsations of the heart, 

 for which we were particularly searching ? In the elaborate 

 " Report upon the English Sparrow " lately issued by the U.S. 

 Department of Agriculture, it is asserted (on p. 109), on the 

 authority of Dr. Leconte, that a Geometer larva {Ennomos 

 subsignai-ia) abundant on the trees growing in the streets of 

 Philadelphia had been exterminated b}- European sparrows ; 

 although this statement is demurred to by the editors of the 

 volume, on the ground that other cai^ses besides the sparrows 

 had probably contributed to this end, it is admitted that " from 

 different parts of New England unimpeachable testimony has 

 come as to the good work done by the sparrow " * in feeding 

 on another Geometer larva {Paleocrita renmta). While it is 

 not pretended that this evidence settles the question as against 

 those who hold that Geometer larvas are protected by their 

 colour and form resemblances, it is contended that it lies with 



* The Sparrow, moreover, unfortunately for the agriculturist, does 

 not confine his depredations to insects. 



