l6 FLEAS, FLUKES AND CUCKOOS 



Although these associations have not been adequately studied, probably 

 all of them will, in time, be recognised as commensal relationships. 



There is another type of nesting association in which birds play a 

 popular and very prominent role in Britain. The erection of buildings 

 with clifT-like fa9ades, overhanging roofs and convenient eaves and 

 beams, has enticed swallows, martins and swifts away from rocky caves 

 and mountain precipices. It has brought them to live and breed in 

 close proximity to man himself. In Africa certain swifts and swallows 

 normally confined to breeding in cliffs which are by no means common, 

 have taken to nesting on buildings of European type — not only on 

 houses but also under bridges and similar structures. Their numbers 

 have since greatly increased. It seems likely that a similar course of 

 events occurred in Britain. Probably at some remote period both man 

 and martins shared the same caves and cliffs around the coast, and the 

 birds eventually followed man and made use of his new and self-made 

 habitations. 



The poets have described the difference in the nesting habits of the 

 various members of the swallow tribe. In England "the temple-haunt- 

 ing martlet" seeks out the purely human dwelling more persistently 

 than the swallow. It favours baronial halls, castles, small towns and 

 villages where it "builds in the weather on the outward wall." On the 

 other hand the swallow "twitt'ring from the straw-built shed" prefers 

 the company of domestic animals. The arrangement of beams and 

 roofing inside farm buildings is better suited to its nesting require- 

 ments. 



Swallows show a slight preference for certain domestic animals. 

 Their prime favourites are cows. Other things being equal they will 

 build in an occupied cowshed rather than a stable or a pigsty, although 

 their love of pigs and horses is also great. Sheep are not so acceptable 

 as companions. 



Human beings obtain great delight from the presence of swallows 

 and martins which nest on their barns and houses. They are not only 

 intrinsically beautiful and graceful birds, but since they arrive in March 

 and April they have become the symbol of spring flowers and sunshine, 

 and the nostalgic hope of better times to come. Man, however, is for 

 ever seeking utilitarian motives for his actions. We find, therefore, that 

 various "reasons" are put forward why the birds should be actively en- 

 couraged. It is frequently asserted, for example, that swallows rid the 

 cowshed of noxious and irritant flies. There is also a widespread 



