BLACK-HEADED GULL 415 



in the early autumn on the slob-lands may be heard utter- 

 ing a high, thin, one-syllabled note varied with a rather 

 faint ' brassy ' squeak. The chorus produced by hundreds, 

 as an intruder approaches the breeding-haunts, is truly 

 bewildering. 



Nest. Black-headed Gulls are highly gregarious during 

 the breeding-season, assembling at their gulleries towards 

 the end of February. The breeding-sites are very diversified. 

 Marshy situations, such as exist along the shores and islands 

 of inland lakes, or flat and open bog-lands, are the usual 

 localities selected. Less frequently marine islands, more or 

 less clad with vegetation, are resorted to, where colonies of 

 this and other sea-birds often exist in close proximity. 

 Sometimes the nests are placed on little mounds amid 

 rushes, surrounded by soft muddy soil, or even by water 

 (Plate XLIL). Others are found in drier situations amid 

 flags, nettles, fallen leaves, and bits of dead sticks (Plate 

 XLIIL, figs. 1, 2, and Plate XLIV.). I have found the 

 nest built into a hollow in the grass, the site resembling 

 that chosen by a Lark or Meadow-Pipit. In addition, 

 nests have been found built on an ancient fort, on isolated 

 rocks in lakes, on the tops of stone beacons, and within 

 a walled hiding-place (Ussher). The nest itself is composed 

 of sedges, grasses, and bits of the surrounding materials. 

 Three eggs constitute the normal clutch, though I have 

 found four and even five in one nest. 1 The ground-colour 

 and the darker markings of the eggs vary to a considerable 

 extent. Some are brownish-green, others light bluish or 

 yellowish-pink, heavily blotched with chocolate-brown. 

 Less frequently they are of a uniform ground-colour. 

 This is seen in Plate XLIV., which is a photograph of 

 a nest containing four dull bluish-white eggs, which, from 

 their extreme similarity in size and colour were very likely 

 the property of a single bird. 



Incubation commences about the end of April or the 

 beginning of May ; three weeks later the young are hatched, 



generally noticed one adult and one young bird together. The same habit 

 applies to other Gulls, a single immature Herring-Gull usually follow- 

 ing an adult. Whether the adult is the rightful parent or not, it is hard 

 to say. 



1 On one occasion I found a nest containing five eggs, three of which 

 were heavily blotched with brown, the remaining two being of a uniform 

 olive-brown colour. The nest most likely contained two clutches. 



