122 TRANSACTIONS-PERTHSHIRE SOCIETY OF NATURAL SCIENCE. 
dissection of many specimens has proved that their food largely con¬ 
sists of beetles and larvae of water insects, some of which are them¬ 
selves the great enemies and destroyers of spawn, so that the Dipper 
is rather beneficial to fisheries than otherwise. When one of them 
is seen diving into the water, and feeding close to a spawning salmon 
there certainly seems to be a case against him, but on investigation 
it has been discovered that the fish, in burrowing in the gravel and 
sand of the river bed, has exposed the embryo insect food of 
the Dipper, who is attracted by instinct to the spot. There is no 
doubt that occasionally he may eat a fish’s egg, but it is exceptional, 
just as the Kestrel, whose normal food consists of mice, beetles, and 
moths, is known sometimes to snatch a chicken from the poultry- 
yard or a young pheasant from the covert side; and the Owls, when 
hunting round the hedgerows in the gloaming, do not always resist 
temptation. Gamekeepers, however, allow no exceptions to their 
inexorable rules, and ruthlessly destroy these and other useful birds, 
notwithstanding that the amount of general good they do, far out¬ 
weighs the evil results of a paltry act of poaching which they may 
from time to time commit. 
Independently of any aggressive action on our part, we must often, 
in the course of our progress, interfere with the laws of Nature, and 
necessarily alter the conditions under which wild animals and plants 
exist, and thus gradually, and almost imperceptibly, the whole fauna 
and flora of the civilized world is shifting and changing under the 
irresistible influence of man ; new species are attracted to places 
where before they were unknown, and others disappear and become 
extinct, while in some localities there is a crowding together which 
tends to an undue predominance of the strong over the weak, and 
the balance of Nature is disturbed. 
In order to restore the lost equilibrium, a certain amount of 
readjustment may from time to time be needed, but should never be 
attempted except with the greatest care and discrimination— a little 
pruning here, and a little extra protection afforded there, may some¬ 
times have the desired effect, but all harsh and severe measures, 
which generally proceed from ignorance, are to be deprecated, for 
outraged Nature sooner or later takes her revenge. In the study 
of birds alone, experience has taught us much. We know, for 
instance, that the wholesale destruction of Owls in a district is often 
followed by a plague of rats and voles, and that in countries where 
soft-billed birds have been annihilated, cornfields and orchards are 
devastated by caterpillars, locusts, and other insect pests. 
This problem of readjustment is a most complicated one, and it 
is rendered all the more difficult owing to the fact that, through want 
of sympathy and lack of general knowledge, there can be no com- 
