INHERITED FEEDING 



HABIT OF HERONS 



John T. Zimmer 

 Bureau of Agriculture, Manila, P. I. 



RECENTLY I had the opportunity 

 to observe a very curious habit 

 ^ possessed by two young herons, 

 which was interesting from the 

 standpoint of its possibly hereditary 

 nature as well as for its peculiarity. 



The birds belonged to the species 

 Pyrrherodia manilensis (Meyen) and 

 were kept in captivity by Alfred 

 Worm of Manila. At the time in ques- 

 tion they were being given their morn- 

 ing meal of partly dried fish, which were 

 thrown to them on the floor of the 

 verandah where the birds were kept. 

 I noticed that they seemed to be having 

 some little difficulty in securing the 

 fish, and that they would peck at each 

 one a number of times before finally 

 obtaining it. Continued observation 

 made it evident that the first efforts 

 invariably fell short of the mark. The 

 consistency of the mistakes in this 

 particular suggested a clue to the ex- 

 planation. Accordingly, to test out the 

 theory, a few fish were thrown into a 

 basin of water, where they sank to the 

 bottom, and offered to the birds in that 

 state. True to expectation, the herons 

 unerringly picked these fish out of the 

 water at the first attempt. 



LIGHT REFRACTION CAUSE OF ERROR 



The explanation which presented it- 

 self to me, is based on the refraction 

 of light. The submerged fish appeared 

 to the observers to be somewhat more 

 distant than they actually were, and 

 hence the herons, in order to reach the 

 mark, were obliged to aim at a point 

 appreciably nearer than the apparent 

 position of the object. This they 

 seemed to do as a matter of course. 



Since, in a wild state, they would secure 

 most of their food from shallow water, 

 food consisting for a large part of prey 

 which would escape if not obtained at 

 the first attempt, this habit of rectifying 

 the aim, to correct for refraction would 

 be extremely advantageous if not in- 

 dispensable. In the present case, how- 

 ever, it seemed to be present at the 

 expense of ability to align the stroke 

 in the direction of actual sight or at 

 least to recognize the necessity for such 

 alignment. 



UNABLE TO PROFIT BY EXPERIENCE 



An interesting feature of the case was 

 the apparent failure of the birds to 

 profit fully by experience. Although 

 they were able to find each object of 

 search after a series of trials, at the next 

 venture they reverted to their original, 

 deflected aim. The persistence of this 

 action leads me to believe that the 

 habit is an inherited trait. I was told 

 that the herons had been fed occasionally 

 in water, since their capture some three 

 weeks previously, but their rations had 

 been given to them for the most part 

 on the bare floor, and as they were 

 taken from the nest when they were 

 less than a week old, there is little chance 

 that the performance was the result of 

 experience, especially since experience 

 seemed to have so little effect in over- 

 coming the difficulty when circimistances 

 demanded it. Whether or not the 

 young herons will acquire greater pro- 

 ficiency in terrestrial feeding as they 

 grow older, remains to be seen. 



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