72 THE SCOTTISH NATURALIST 



authors. Fluctuation in numerical strength is a feature 

 common to most gulleries ; what for a series of years was 

 a strong one, may dwindle to a few pairs, or even be' deserted 

 altogether for a time, and then become populous once more. 

 The nature of the season (wet or dry), drainage, construction 

 of new reservoirs, protection, persecution (including wholesale 

 egg taking), and possibly to some extent migration, all tend 

 to produce these results. Within recent years there has 

 been an increase in the number of gulleries in the area ; 

 and it would seem that a substantial increase in our Black- 

 headed Gull population as a whole has taken place, though 

 to what extent it is difficult to say. At the best, however, 

 natural increase can under present conditions be but a slow 

 process, so few are the offspring most colonies are given the 

 chance of rearing. At the close of the breeding season 

 I have seen a colony of some 250 Gulls on its return to the 

 coast include scarcely half a dozen young birds ; but doubtless 

 this is an extreme case. The population of a large gullery 

 is a difficult matter to decide and a rough estimate is usually 

 all that can be given. In the presence of such an animated 

 scene as a large gullery presents at the height of the breeding 

 season, the tendency is to exaggerate the number of birds,^ 

 and it may be that in my endeavour to avoid this error I 

 have erred in the opposite direction though I hardly think 

 so. Assuming that my figures are not greatly at fault, 

 the aggregate present strength of the Black-headed Gull 

 colonies situated in the Forth area would appear to be in 

 the neighbourhood of 5000 pairs. 



North-eastern Berwickshire. 



No present or past breeding place of the Black-headed 

 Gull in the county of Haddington (East Lothian) can be 

 traced ; but in the adjoining north-eastern corner of Berwick- 

 shire, where the boundary between the Forth and the Tweed 

 areas runs out to St Abb's Head, a small colony has long 

 been known to nest on the moors between Coldinghavi Loch 



^ See, for instance, the case of the Gannet as investigated in Mr 

 J. H. Gurney's book on that species. 



