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THE NESTING OF THE COMMON TERN AND BLACK- 

 HEADED GULL IN COLCHESTER HARBOUR. 



By Thomas Hepburn. 



I was enabled during the early summer of 1909 to make 

 some extended observations on a mixed colony of Common 

 Terns {Sterna fiuviatilis) and Black-headed Gulls (Larus ridi- 

 bundus) which were nesting in Colchester Harbour. I will not 

 define the position of the colony more closely. 



Although I only located the colony last year (1909), I had 

 previously, in the late summer of 1907, seen a large mob of 

 Common Terns resting on the mud of one of the tidal creeks — 

 at a spot, as it turned out, not far from their nesting site. The 

 composition of the mob, adult birds and the young of the year 

 together, and the large number of individuals forming it, 

 suggested the members of a colony gathered together previous 

 to their autumn migration. During the summer of 1908 I made 

 notes of several individuals of the same species seen in various 

 localities of the estuaries of the Colne and Blackwater. But I 

 could obtain no information locally, either from fishermen or 

 shepherds, of any spot where they nested. This, however, I 

 found myself last spring by a careful and systematic exploration 

 of the creeks and saltings of the neighbourhood in which I saw 

 the big mob in 1907. Even the gentleman to whose farm the 

 land on which the birds nested was attached was not aware 

 of their presence. Through his courtesy I was enabled to 

 pay many visits to the colony, and carry out some detailed 

 observations amongst the nesting birds during the summer 

 of 1909. 



Their nesting site was situated entirely outside the marsh 

 walls. It was therefore subject to being submerged by the tide, 

 if ever the level attained was high enough. I have been told 

 that tides occasionally do cover the whole area, but during the 

 months of my observations — May, June, and July — no tide 

 Zool. 4th ser. vol. XIV., April, 1910. m 



