NON-INDIGENOUS BRITISH BIRDS. 323 



than a hollow in the sand or hard ground, with perhaps 

 a few bits of dry grass by way of lining, and is frequently 

 placed in a very exposed situation. Whilst one bird is 

 sitting, the other keeps in the vicinity to give notice of 

 any approaching danger. The bird is a light sitter, and 

 usually slips off the nest the moment it is alarmed, 

 taking refuge in the water, where it is joined by its 

 mate. The note of this Diver during the breeding 

 season is a wild unearthly scream. 



Range of egg colouration and measurement: 

 The eggs of the Great Northern Diver are almost invari- 

 ably two in number, but it is said three have been found 

 in one nest. I consider this very doubtful. They vary 

 in ground colour from russet-brown to olive-brown, 

 spotted with dark blackish-brown, and with underlying 

 markings of paler brown. The spots are not numerous, 

 and mostly congregated on the major half of the <^gg, 

 ranging from the size of a buck-shot downwards. The 

 underlying markings are small and (qw. Average 

 measurement, 3*5 inches in length, by 2*5 inches in 

 breadth. Incubation, performed by both sexes, lasts 

 about a month. 



Diagnostic characters : The eggs of the Great 

 Northern Diver may be generally distinguished from 

 those of the Red- and Black-throated Divers by their 

 larger size, but exceptionally small eggs cannot be separ- 

 ated from those of the latter species. Careful identifica- 

 tion is therefore necessary. From eggs of the White- 

 billed Diver I am unable to give any character by which 

 they may be distinguished, as the eggs of that bird still 

 remain unknown to science. {Cojif. Appendix I. p. 344.) 



