1388 Birds. 



numbers of the Raptores, especially of those which nest in the district, 

 the same cause has greatly increased the numbers of the smaller spe- 

 cies of perchers, which find in the extensive covers a safe retreat from 

 the depredations of birds of prey, and from the still more mischievous 

 attacks of bird's-nesting boys. 



The closer weeding of the fields, consequent upon agricultural im- 

 provements, has interfered a little with some of the ground-nesting 

 birds, but this probably does not apply to many species. 



Of the regular migratory birds of Norfolk, those which arrive 

 in spring, nest in the county and depart in autumn, are thirty-three in 

 number, nearly half of them belonging to the family of the Sylviadae. 

 With the exception of certain species which also visit us in spring, 

 but proceed to more northern breeding places, these are perhaps more 

 regular in their appearance than birds of any other class. We believe 

 that they also travel in small flocks, and chiefly during the night. 

 The Hirundinida are well-known to congregate before departure, and 

 we have observed the sand-martins to collect on the coast in immense 

 flocks previous to their autumnal migration, the beach appearing at a 

 short distance perfectly black with their numbers. 



The line of division between the winter residents, and those birds 

 which annually pass through this district in spring, on their passage 

 to, and in autumn on their return from, their breeding places, cannot 

 be permanently drawn with correctness, inasmuch as the movements 

 of these divisions depend much upon the temperature, and perhaps in 

 some measure on the prevailing winds of the particular season ; and 

 that, not so much in our own, as in more northern latitudes. Amongst 

 the autumnal migrants to our coasts, the occasional irregularity in the 

 numbers of the common buzzard, and still more in those of the rough- 

 legged buzzard, are curious and worthy of especial attention. These 

 birds are both regular visiters, but not in large numbers. In the au- 

 tumn of 1839, the latter species was unusually plentiful, and we had 

 an opportunity of observing that the same migration extended over 

 part of Germany ; which makes it probable that the birds came from 

 a considerable distance, and that their appearance was not attribut- 

 able to their having been driven from their usual route by any acci- 

 dental cause. In the autumn of 1845 on the contrary, the rough-legged 

 buzzard was hardly seen, whilst the deficiency was to a certain ex- 

 tent counterbalanced by an increased influx of the common species. 

 These variations are at present unaccountable, as we can neither con- 

 nect them with change of temperature, nor with any deficiency 



