232 THE SHELDUCK AND SURFACE-FEEDING DUCKS 



need : after frost the only other factor powerful enough to drive them 

 from fresh water is persecution at the hands of sportsmen. When 

 they are constantly harassed by day, such as live within reach of the 

 sea repair thither daily at dawn, returning at night to their chosen 

 haunts to feed. As with the species already considered, it would seem 

 that these nocturnal meals are partaken of rather from necessity than 

 choice : persecution at the hands of man driving them to seek the 

 cover of the darkness as a means of security against surprise, which is 

 the more easy when the attention is distracted by the search for meat. 

 This, however, is by no means clearly established. It is quite possible 

 that, at any rate during certain times of the year, they may feed by 

 choice at night. For it must be remembered that much of the food 

 of the surface-feeding ducks is of an intangible character, invisible to 

 the birds themselves, consisting as it does of microscopic animal and 

 vegetable organisms, many of which may be of the kind known as 

 negatively heliotropic, that is to say, shunning the daylight as a 

 certain personage is said to avoid apple-dumplings and therefore 

 obtainable only during the hours of darkness. These highly nutritive 

 but invisible bodies are obtained, as everybody knows, only by passing 

 large quantities of water rapidly through the mouth by the process 

 known among fen-men as "bibbling." The solid particles are lodged 

 on the fleshy, sensitive tongue, and the water is strained off by the 

 fringes along its sides and the lamellae bordering the beak. And 

 such " small deer " can be captured as well by night as by day. More 

 observations are needed on this subject, and it may prove that per- 

 secution is only partly responsible for these nocturnal habits. 



By day teal will rest for hours motionless, in pensive mood, or 

 asleep with the head tucked away amid the scapulars ; but if surprised 

 they take flight with amazing suddenness, shooting straight up into the 

 air without preliminary warning, as from a steel spring. They are no 

 less remarkable for the skill and speed with which they change the 

 direction of their flight, even when in full career, for they can turn 

 and twist with the ease of a flock of dunlins, and often, when 



