NON-INDIGE.YOUS BRITISH BIRDS. 325 



reeds, sedge, and other aquatic vegetation. The nest is 

 generally a floating structure amongst the reeds or 

 rushes, but is frequently placed on a hassock of sedge 

 or coarse grass at some distance from the open water. 

 The nest is moderately large and compact, and com- 

 posed of half-rotten sedges, rushes, reeds, and aquatic 

 plants massed and heaped together, the cavity contain- 

 ing the eggs being lined with finer and drier material, 

 leaves of the rushes, bits of reed, and dry grass. It 

 would appear that in some districts more gregarious 

 instincts prevail ; for Canon Tristram states that he 

 found a densely-crowded colony of this Grebe on Lake 

 Hallo ula in Algeria, the nests being so close together 

 in some places as almost to touch each other. Some 

 of these nests were made on foundations that reached 

 from the bottom of water more than a yard in depth. 

 When leaving the nest voluntarily the parent bird 

 carefully covers the eggs with pieces of moss or wet 

 grass to conceal them from view. 



Range of egg colouration and measurement : 

 The eggs of the Black-necked Grebe are four or five in 

 number. They are rough in texture, almost as much 

 pointed at one end as the other, and yellowish-white, 

 sometimes with obscure traces of the green interior 

 showing through. Average measurement, 1*8 inch in 

 length, by r2 inch in breadth. Incubation, performed 

 by both sexes, lasts from twenty-one to twenty-four 

 days. 



Diagnostic characters : The eggs of the Black- 

 necked Grebe are readily distinguished from those of 

 the Little Grebe by their larger size, but are absolutely 

 indistinguishable from those of the Sclavonian Grebe. 

 They can be separated from those of the Red-necked 

 Grebe by their smaller size, the two measurements on 

 any single Qgg never overlapping. It should be remarked 



