64 BIKDS OF NORFOLK. 



coarse herbage of their own collecting and added to 

 more or less throughout the time of incubation. The 

 interior is composed of somewhat finer materials, mixed 

 with their own down and feathers. Though generally 

 high enough to escajDC the effects of any ordinary 

 flood, they have been known to raise them suddenly, — 

 either collecting materials of their own accord or using 

 such as the forethought of the marshmen may have 

 supplied,— and thus, by a marvellous instinct, as in 

 the case recorded by Yarrell, anticipate an extra- 

 ordinary high tide.^ At such times, both birds are 

 employed in the work, the male collecting materials and 

 its mate arranging them and shifting her eggs. The 

 process, as observed by Rich on more than one occasion, 

 appears to be as follows : — The fresh stuff is piled up on 

 one side of the nest, and having been roughly laid with 

 the bill, is flattened down with the crown of the head ; 

 the eggs are then carefully rolled on to the higher surface 

 by means of the head and beak, the under part of the 

 lower mandible being inserted under each, and the same 

 course is then adopted on the other side, and lastly, 

 having raised the centre in proportion, the eggs are 

 returned to their proper position. The eggs, however, 

 are not exposed during all this time, but are covered at 

 intervals by the female to keep them warm, and this even 

 when the waters are rising rapidly. t 



* "Waterton, in his chapter on the mute swan, in the second 

 series of his " Essays," describes his own swans as constantly and 

 needlessly raising their nests, which were placed " on an island 

 quite above the reach of a flood," even on one occasion using " two 

 huge bunches of oaten straw," supplied for the purpose. In this 

 case, one still recognises an instinctive impulse, even though 

 uncalled for. A " propensity," in fact, as Paley describes it, " prior 

 to experience and independent of instruction." 



f The same means is not unfrequently adopted, under similar 

 circumstances, by coots and water-hens ; and black-headed gulls 

 are known to raise their nests at times. 



