BRITAIN'S BIRDS AND THEIR NESTS. 39 



shown, however, that this is accomplished by a partial 

 moult at that season. 



The Black-headed Gull could not well be termed a 

 'Sea-Gull,"" for it is not to any extent a marine species. 

 It may, it is true, be found about our coasts at all 

 seasons, but chiefly where there are sandy shores and 

 sheltered estuaries. In summer many of its haunts are 

 far from the sea, islands on inland waters being favourite 

 nesting resorts. Still more typical haunts are the marshy 

 edges of meres or lochs. There the muddy pools and the 

 stretches of quaking turf form some protection against 

 many of its enemies, including man, its worst. In the 

 southern and south-western counties of England, breeding 

 colonies of Black-headed Gvdls are few and far between ; 

 but some of them are of great size, although not so great 

 as a few decades ago. Scoulton Mere in Norfolk is 

 perhaps the most famous nesting-place. Fifty years ago 

 16,000 eggs were taken for eating purposes from that 

 colony alone in a single season ! In Wales, in the Lake 

 District, and in the north of England generally, colonies 

 become more numerous. In Scotland, colonies are very 

 frequent, even up to the Hebrides and the Shetland Isles. 

 In Ireland the species is everywhere abundant. 



In winter the Black-headed Gull is found on the 

 Thames at London, and at other places where it is not 

 found to any extent in the breeding season. But the 

 numbers throughout the countiy in winter can only 

 represent a fraction of those that nest with us. The 

 migrations of birds like this — ' partial migrants," we call 

 them — are rather difficult to study, as it is impossible to 

 note their arrivals and departures owing to the presence 

 of some members of the species throughout the year. An 

 interesting method of study which avoids this difficulty is 

 that of recording the wanderings of marked individual 



