INTRODUCTION. 55 



margins of the waters, and scarcely intrude on the 

 great field itself, but stalk among- its shallows, and 

 feed among the wreck brought down by its streams- 

 or left by its tides, and upon the various animal 

 life periodically uncovered by the same agency. 

 In point of utility, these birds stand more as a 

 check upon the tribes of being's which serve for 

 their support, than as being directly beneficial. 

 The flesh of some is used for food, and is both 

 highly flavoured and wholesome; and the pursuit 

 of a few in the fenny countries, with the collection 

 of their eggs for the London and some other great 

 markets, for a month or two, give employment to 

 the fen-men. Others are domesticated, and walk 

 about the public markets, or in warm countries 

 through the towns, ridding them of all offal and 

 animal refuse, which would so soon taint the air, 

 and tend to increase the sickness or epidemical 

 diseases. But their great place seems to be for 

 the reduction of the numbers of reptiles, which 

 abound in the districts where the larger typical 

 species are most numerously found. The habits 

 of patient watchfulness among all the Ardeadce or 

 Herons, their quick sight, ravenous appetite, and 

 great power of digestion, render the quantity that 

 can be devoured in a short period very great, and 

 they place a powerful restraint upon creatures 

 which reproduce most rapidly. The other families 

 are chiefly insectivorous, or support themselves 

 also on molusca and the various marine life ; and 

 during the summer on our higher located pastures. 



