Are birds easily deceived ?



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ARE BIRDS EASILY DECEIVED?


By Arthur G. Butler, Ph.D.


I confess that I was puzzled as to the character of the stick-

insects which Mr. Brook mentioned as recommended by Mr. Seth-

Smith for bird-food ; I even wondered at the time whether certain

stick-like caterpillars might not be intended: it is therefore satisfactory

to know that the genuine Orthopterous insects were meant, because

it bears out my own contention that insects are only protected to

a moderate extent by their mimetic character. It is evident that

Carausius is not distasteful, or it would not he greedily devoured,

and it seems probable that the same may be true of other stick-

insects.


We must therefore conclude that where there is abundance

of insect-food a bird does not take the trouble to examine a stick- or

leaf-like object, in order to decide whether it is animal or vegetable.

On the other hand, if an insectivorous bird has been unable to obtain

much insect-food, or is hungry, it closely examines every leaf and

twig, and thus speedily discovers its character, as I pointed out as

long ago as December, 1889 (‘Ann. Mag. Nat. Hist.,’ p. 472), where

I recorded the fact of giving an example of the leaf-like moth

(Phlogophora meticulosa ) to a Liolhrix on September 25th, 1887,

which, after carefully examining it and probably observing its legs,

tested its character with a peck and then devoured it. I ought,

however, to have said that I suspended the moth in an inconspicuous

corner of the cage when the bird was not looking : I did not otter it

to him, or he would probably have accepted it without hesitation.


Birds have such excellent eyesight that they are not readily

deceived, and anybody who has watched our Tits and Warblers

carefully examining the twigs and leaves of trees and shrubs in their

search for food, or our winter residents turning over the fallen leaves

which carpet the earth, must be well satisfied that little can escape

their vigilance. If their resemblance to twigs alone served to protect

the caterpillars of certain Geometrid moths (loopers), I do not think

many would escape ; hut, as I have pointed out elsewhere, they are

so tough and rigid that a small bird is unable to shake and beat them

to a pulp as he does the softer type of smooth caterpillar. The



