64 BRITISH BIRDS. 



They are not Irish. The slates and mica schist might come from 

 Anglesey, the Isle of Man, or Scotland. We must not forget that the 

 island is covered with glacial deposits which contain erratics from many 

 localities, and that makes it increasingly difficult to trace their origin. 

 I am sorry the examination of the stones does not lead to definite results 

 from your point of view." — Eds. 



COMMON TERNS ON THE HOLYHEAD SKERRIES. 



It is generally supposed that these birds do not breed on the 

 Skerries, and that the rocks are occupied during the breeding 

 season exclusively by Arctic Terns and a few Roseate Terns 

 (c/. H. E. Forrest, VerL Fauna N. Wales, p. 375). That this 

 is not the case has recently been proved by her Grace the 

 Duchess of Bedford, who has been good enough to forward 

 me a Common Tern {Sterna fluviatilis), which killed itself 

 against the telephone wire whilst she was visiting the colony. 

 Her Grace added, " several were seen." 



Heatley Noble. 



ABNORMAL EGGS OF BLACK-HEADED GULL. 



On May 15th, 1908, I took a nest, with its clutch of three 

 eggs, of the Black-headed Gull {Larus ridibundus) from a 

 lake island in Ireland where this Gull was nesting in 

 numbers. It is well known that the ground colour and 

 markings of their eggs vary to a considerable extent, these 

 are of a pale greenish blue — the two largest almost without 

 markings, the smallest with a few brownish blotches. The 

 contents of the eggs were fresh and, as far as I could judge, 

 normal in appearance, as are also the shells, with the exception 

 of the smallest, which appears to be rough and of a some- 

 what friable nature at its pointed end. They measure 

 1-4 X 1.1 in., 1.6 X 1.2 in., 1.7 x 1.2 in. Patten in his 

 "Aquatic Birds" gives the average measurements of the 

 eggs of the Black-headed Gull as 2.2 x 1.5 in. I beheve 

 complete clutches of abnormally small eggs of this species are 

 not common. 



Herbert Trevelyan. 



INCUBATION-PERIODS IN SEA-BIRDS. 



During the spring and summer of 1907 Mr. F. G. Paynter 

 made some experiments as to the duration of the incubation- 

 period of certain sea-birds at the Fame Islands by placing 

 the eggs in a hot-air incubator. Mr. Paynter describes his 

 experiments in " Country Life " (March 21st, 1908, p. 409), 

 and we give below the results arrived at, and add for the sake 



