414 THE BIOLOGY OF BIRDS 



the news to Rome, as, in later days, the news of the victory 

 at Waterloo was brought to England by pigeons some days 

 in advance of the official courier." . . . Penguin oil from the 

 Falkland Islands has a more than local utilisation. . . . The 

 sinews of birds are used by certain remote tribes in place of 

 thread. . . . But the indirect utility of birds, especially in 

 keeping down injurious insects, is much more important 

 than the direct utility. As Michelet tersely put it : 

 " L'oiseau peut vivre sans I'homme, mais I'homme ne peut 

 vivre sans l'oiseau." 



§ 7. The Inter-Linking of Lives 



The main theme of this chapter — the intricate inter- 

 linking of lives — may be illustrated by Dr. Ritchie's story 

 of the Black-headed Gulls on the White Moss, near West 

 Linton, in Peeblesshire. In 1890 it was a typical heather 

 moor, with peat and moisture underneath. In 1892 or 

 1893 a few pairs of gulls came to nest on the Moss, and were 

 encouraged ; in 1897 there was a populous colony ; in 1904 

 the number was estimated at 1,500 to 2,000 pairs. The 

 vegetation round about underwent a remarkable change ; 

 the heather was replaced by coarse grass, that by rushes, 

 and these, again, by a forest of docks. 



These changes were partly due to the fertilising of the 

 soil by food-refuse and excreta from the gullery, and partly 

 to the puddhng of the surface by the thousands of feet and 

 to the surface accumulation of the crowded nests, " so that 

 superficial water was retained, and the peat bed with con- 

 cealed and deep moisture was transformed into a surface 

 marsh." 



But more changes were in process. The grouse dis- 

 appeared from the moor and teal ducks came, attracted by 

 the marsh and the rushes. A single flock, with as many 

 as seventy ducks, was seen when the gullery was as its 

 height. 



Fifteen years passed, and man interfered again, rapidly 

 ousting the gulls from their tenancy of the White Moss. 



