COMMON AND ARCTIC-TERNS 85 



Harbour, Mr. A. Hepburn 1 found few nests with no lining. Mr. 

 Jourdain found nests of the common-tern in Holland all lined. Mr. 

 Hepburn also made a discovery which probably explains much of the 

 contradictory evidence on this subject in respect to both species. It 

 was that the lining was accumulated gradually by the sitting bird. 

 In the majority of cases a " slight " lining was recorded on the first 

 finding of the nest, and a " thick lining " or a " big pad " on the visit a 

 week later. This was particularly the case after a wet week, when a 

 number of nests were made up with fresh material placed on top of 

 the old. I have noted the same in the case of the gannet, and it is 

 common, Mr. Farren tells me, to most or all the Waders, and no 

 doubt also to all species with similar nesting-habits. The fact 

 possibly explains why at the Fames on May 29, when the Arctic- 

 terns were just beginning to lay, I found very few lined nests among 

 the thirty or forty I examined, and these few contained only some 

 odd stalks that may not, indeed, have been put there by the birds, 

 whereas of thirty nests of the same species examined at Walney at the 

 end of June I found only two without lining. Some nests unquestion- 

 ably remain unlined. The one shown on PI. XLIII., from which young 

 were hatched, is an example. The average proportion of lined and 

 unlined has, however, yet to be established. 



In the choice of material for the lining the species show no per- 

 ceptible difference. They take as a rule what is near at hand, but 

 why from the material available in one and the same colony certain 

 individuals choose say pebbles, and others bents, or why, again, some 

 dispense with a lining altogether, are questions that still beg a 

 satisfactory answer. 2 Occasionally terns will neglect material near 

 the nesting-site for less accessible. On the rock stacks at Rhos Colyn, 

 Anglesea, where Arctic-terns breed, Messrs. Coward and Oldham 

 noted that the only vegetation was lichen. Several made their nests 



1 Zoologist, 1910, 140. 



1 For a discussion of them see British Birds, i. 373 (W. P. Pycraf t) ; ii. 78, 101 (F. B. 

 Kirkman). 



