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swallows, and the authors remark " it is interesting from the 

 biological point of view, that they should readily take flies of 

 a brilliant canary-yellow colour such as they can never have 

 seen before. A few of these coloured flies that happened to 

 drop into the water were also seen to fall a prey to fish." Dr. 

 S. Monckton Copemaii, F.R.S., had kindly sent a few further 

 details concerning the behaviour of the swallows : — 



"Local Government Board, Whitehall, S.W., 



"February 9, 1912. 

 "The swallows seemed to know when we were going to 

 let loose the coloured flies ; for although on our arrival there 

 might not be a swallow to be seen over the river, no sooner 

 had we let loose one lot of flies than there were usually a 

 number to be seen, flying up and down in front of the 

 liv] 



wharf-staging from which we dispatched our flies. When the 

 second lot was loosed the swallows at once proceeded to 

 retrieve the flies while the latter were crossing the river 

 in various directions; — the swallows never seeming to pause, 

 but retrieving the flies unerringly while themselves in full 

 flight." 



These interesting experiments showed the danger of a 

 conspicuous colour when associated with palatability. 



2. The far-reaching distance of birds' vision was indicated 

 in an article to which his attention had been called by Dr. 

 F. G. Penrose : — " Hawk-catching in Holland, I." in " Country 

 Life" for August 7, 1909 (p. 185). The article described the 

 ancient methods which are still practised at the Dutch village 

 of Valkenswaard (Falcon's Heath). One important element 

 was the use of a tethered great grey shrike to act as a sentinel. 

 " Now as soon as any bird of prey appears — even far beyond the 

 ken of any human observer — this sentinel shows evident signs of 

 terror, which increase if the enemy should come nearer. ( )ld 

 Adrian Mollen, father of the great master of the art, used to 

 say, that, by the gestures and sounds of alarm of the shrike, 

 he could sometimes form a pretty correct guess as to the size 

 and species of the hawk ..." (p. 187). The words here 

 printed in italics were good evidence of the great distance at 

 which birds could recognise the details of form and movement. 



