44 



dus niet door den mensch met behulp van een rekensommetje 

 vooruit te bepalen is, zooals sommige menschen, die meer théorie 

 dan praktijk hebben, ons zouden willen doen gelooven, al gebi'uikten 

 zij voor hun rekensom nög zoo geleerde termen! 



Tot in de kleinste détails was alles met den- Chil. geelbektaüng 

 en het Z. Afrik. roodbekje gelijk aan het vroeger gebeurde met 

 wintertaling X pijlstaart-eend, en toch waren de uitko nisten 

 geh eel anders! 



Gooilust, Maart 1923. " F. E. Blaauw. 



Remarkable behaviour of the Whooperswan. 



Among other statements about some interesting instincts and 

 habitformation of birds '), I gave some communications about the 

 different ways in which some birds seek worms, either by „quaking" 

 by means of one leg, kept in front, as Vanelliis vanellus (L.) does, 

 or l)y tripping or trampling on two legs, as may be seen of Lams 

 argentatus (Briinnich), Tadorna tadonia (L.) and T. tadornoides Sclat. 



In connection herewith may be pointed to a remarkable behaviour 

 of Cygnus cijgniis L., which species breeds almost every year in 

 the gardens of the Royal Zoological Society „Natura Artis Magistra" 

 in Amsterdam -). 



As soon as the young ones are hatched, the couple with their 

 offspring are .put into a separate paddock, which contains a round 

 basin of about 60 c.M. deep, with an almost perpendicular wall. 



If live Daphnia's and Cyclops are put into this basin, the mother 

 and her swanlets are able to slabber this food at the surface by 

 means of their „sieve-bills". 



But when these small Crustaceans sink deeper, the swanlets 

 however can by no means get at them. 



Now our keeper and myself have repeatedly observed, that the 

 mother-swan, on entering the basin with her young ones, and 

 finding no Daphnia's at the surface, made downward 

 trampling movements with both legs (so not back- 



1) „Ardea", Jaargang XI, 1922, Afl. 1, pp. 23 — 40. Eenige morkwaardige 

 instincten en gewoontevormingen by vogels, door A. F. J. Portielje. 



2) See about this subject: „Ardea", Jaargang I, 1912, p. 87. Eenige mede- 

 deelingen over Cyynus cygnits L., door Dr. C. Keebert. 



