206 OUR BIRD ALLIES. 
Att the Gulls are more or less useful as scavengers, 
scouring the surface of the sea, and there performing 
much the same duties as are discharged by the crow, 
the burying-beetles, and the blow-flies upon the land. 
To transmute death into life, to remove all that is 
displeasing to the senses and injurious to health, and 
to maintain the highest possible degree of purity 
alike upon land and sea,—such is the task of the. 
gulls and their allies, a task which we ourselves 
cannot possibly perform, and which cannot be 
neglected without the absolute certainty of dire and 
widespread consequences. 
Some of the gulls, however, must be considered as 
doubly the benefactors of man, not only bearing 
their share in the never-ceasing work of purification, 
but aiding the farmer to a very considerable degree 
by the slaughter of the various creatures injurious to 
agriculture. Near the sea, large flocks of these birds 
are often—or, rather, generally—to be seen following 
the plough, industriously searching for the grubs, 
worms, and insects which are thrown up, and de- 
vouring them before they can succeed in burying 
themselves once more. The number of mischievous 
insects thus destroyed in the course of the year must 
be almost incredible, and the success of agriculture 
near many parts of the coast is undoubtedly due, 
in great measure, to the ceaseless efforts of these 
valuable birds. 
One of the most useful members of this most 
useful group is the Black-headed Gull, a very plentiful 
