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 ‘eulleries 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 XLII.). Others are found in drier situations amid 
flags, nettles, ance leaves, and bits of dead sticks (Plate 
XULIII., figs. 1, 2, and Plate XLIV.). I have found the 
nest built into a hollow in the erass, 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 1s 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! The eround- colour 
and the darker markings of the eggs vary to a considerable 
extent. Some are brownish- ereen, 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 i 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. 
! 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. 
