GOMMENSALISM I7 



superstition in Britain that if the swallows' nests are robbed of eggs the 

 cows give bloody milk. So far there is no evidence that man benefits, 

 either indirectly through the well-being of his stock or directly, except 

 aesthetically, from the close proximity of the birds, and any advantages 

 appear entirely on the side of the martins and swallows. Nevertheless, 

 if we admit the psychological element it is evident that the relationship 

 entails mutual benefit. 



Much the same may be said of the curious ties that link the robin 

 and man in Britain. The bird receives all the tangible advantages, 

 which chiefly consists of food deliberately or accidentally provided during 

 the critical winter months. Man, on the other hand, obtains great 

 aesthetic satisfaction and pleasure from the bird's song and appearance, 

 but most of all from its tameness. 



^' But what gives me most joy is when I see 

 Snow on my doorstep printed by their feet.'' 



In many other regions of Europe the robin is a shy woodland species 

 which shuns human habitations and is ruthlessly trapped, persecuted 

 and eaten by man. Fairly reliable figures show, for example, that 

 twenty thousand robins were killed for the table in one season near 

 Toulon in France. In England to-day a man known to eat robins would 

 risk social ostracism. Here we have the interesting phenomenon of two 

 species exhibiting a commensal relationship in one part of their geo- 

 graphical range and a predatory relationship in another. 



There are several birds in Britain which enjoy less well marked 

 commensal relationships with man. Thus, jackdaws, rooks and gulls 

 regularly follow the plough, and sparrows, wood-pigeons, and stock- 

 doves obtain a considerable proportion of their food from agricultural 

 crops. In British seas and on the Newfoundland Banks the fulmar and 

 great shearwater follow the trawlers, and round the coasts where the 

 fishing vessels discharge their catches, various species of gulls are 

 commensals of fishermen. During the last sixty years many black- 

 headed gulls, herring-gulls and common gulls have changed their 

 habits in the winter. When the cold weather sets in they move up the 

 rivers into the large towns where they obtain food in the parks and 

 along the water fronts from the passers-by. These movements are 

 diurnal and towards evening the gulls can be seen flying away to roost 

 in quieter surroundings. 



