TO ORKNEY AND SHETLAND. 115 



impossible to tell from outward appearance the 

 sex to which each belonged ; and that this differ- 

 ence does not depend upon age, is proved by the 

 circumstance of my having frequently taken the 

 full-fledged young birds of a dark brown colour, 

 the parents of which were white-breasted, and, on 

 the contrary, light-coloured young birds from 

 dark-coloured parents ; the light-coloured birds 

 however are not so numerous as the dark ones. 

 Difference of colour appears to have no effect in 

 their associating together in the breeding-season ; 

 they mix indiscriminately : I have seen instances 

 of two of these birds pairing together, the one 

 dark brown, the other much lighter with a white 

 breast ; two both light brown; and again two both 

 dark brown. 



Procellaria glactalis, Linn. Malemuk 

 Fulmar Petrel. — This bird occasionally visits 

 Shetland during the winter in stormy weather ; I 

 am not aware of its having been seen in Orkney. 



Puffinus Anglorum, Ray. Lyrie*. Manx 

 Petrel. Shearwater. — The Shearwater is tolerably 

 plentiful both in Orkney and Shetland during the 

 summer season. Considerable numbers breed in 

 Foula and Unst in the latter country, and in 



