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 beings 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, 
