362 BIRDS OF TUNISIA 



obtainable, large numbers of the bird are unfortunately destroyed in 

 Tunis, as in many other places, for purposes of millinery. 



Essentially gregarious, it congregates together, as above mentioned, 

 in vast multitudes on migration, when it may be found on the sea- 

 shore as well as on the borders of lakes and marshes. Its flight and 

 movements are extremely light and graceful. Its note is rather a 

 shrill " krik, krik." It feeds chiefly on small fish, water-insects 

 and their larvae, as well as on worms and tadpoles. 



Subfamily LAEIN^. 



LARUS EIDIBUNDUS, Linnffius. 



BLACK-HEADED GULL. 



Larus ridibundus, Linn. Syst. Nat. i, p. 225 (1766) ; Malherbc, Cat. Bais. 



d'Ois. Alg. p. 22 (1816); Whitakcr, Ibis, 1895, p. 106 ; Saunders, Cat. 



Birds Brit. Mas. xxv, p. 207 ; Erlangcr, J. f. 0. 1900, p. 74. 

 Gavia capistrata, Loche, Expl. Sci. Alg. Ois. ii, p. 193 (1867). 

 Xema ridibunda, Kocnig, J.fO. 1888, p. 290; id. J.f. 0. 1893, p. 101. 



Description. — Adult male, spring, from Tunis, North Tunisia. 



Entire head coffee-brown ; a narrow line above and behind the eye 

 white ; nape and neck white, shading into pearl-grey on the mantle, back, 

 scapulars, secondaries and most of the upper wing-coverts ; primaries white, 

 tipped, and on the inner webs broadly margined with black, the outermost 

 primary with the outer web almost entirely black ; rump, upper tail-coverts 

 and tail white ; under parts below the throat white. 



Iris hazel ; edge of eyelid, bill and feet red. 



Total length 15-50 inches, wing 12-75, culmen 1-80, tarsus TSO. 



Adult female similar to the male, but rather smaller. 



In winter the adult has the head and throat white, with a small dark 

 patch in front of the eye, and a larger patch behind it, otherwise the plumage 

 is as in spring. 



The dark hood, as a rule, begins to appear at the end of February or 

 beginning of March, and is completely assumed by the middle or end of 

 April. Occasionally, however, it is assumed much earlier, even in mid- 

 winter. 



Young birds vary considerably in plumage according to age. The prin- 

 cipal signs of immaturity are, however, to be found in the white or whitish 

 head, the brownish marking of the upper parts, the brown quills and the 

 brown band at the tip of the tail. 



