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Bi-1228            United States Department of Agrieulture 
Sept. 132               Bureau of Biological Survey 
Washington, D. C. 
FOOD HABITS OF FISH-EATIRG BIRDS 
Fish-eating birds, like most other birds, feed on what is com. on and 
easy to get. Their choice of food is so largely governed by aveiltibility
that 
in most waters they will got only a smnll proportion of game or.c- r.ercial*

fishes, as it is in small proportions that those fishes occur. Yt: only are

the more valuable fishes rare as compjared with the noncorerciol species,
but 
they also usually inhabit deeper water and are swifter, Henoe they are harder

to catch than rzmy of the so-caulled coarse fishes. , In some trout streams

t.h.ere may be a preponderance of trout over other fishes, but even in these

streams the birds often find and. capture water insects, crustace-cns, frogs,

snck-es, and other creatures more easily than they do the elusive trot. 
Wondering what becomes of the immense numbers of. trout fry that are 
planted in streams, anglers naturally attribute their disa lpearance to the

enemies that are most obvious, and they are particularly likely t3 blame
the 
larger fish-*eating birds, such as the herons. Studies of trout streams by

the Biological Board of Canada, however, show that the greatest losses in
trout 
fry are caused by enemy and competitor fishes. Fez people realize what serious

destroyers of spawn there are anong the fishes themselves-such species, for

instance, as sticldebacks, sculpins, suckers, and minnows. 
After hatching, the little fishes are decimated by cannibalistic attacks

of which none are worse than those of the trout and other game fishes them-

selves. Besides the fish enemies of fishes the streams teem with insect and

other enemies, such as the larvae of the predad uns diving beetles, or "water

tigers," nymphs of dragon flies, giant water bugs, and crawfishos. All
such 
enomes in turn are preyed upon by birds, and it is probable, except at fish

hatcheri es, that in most cases fish-eating birds =ore than maee up for the

harm they do in eating valuable fishes by their destruction of natural enemies

of the whole fish tribe. 
Illustrating the food habits of fish-eating birds by those of the great 
blue heron, which is one of the largest and most conspicuous of the group,
it 
rlay be reported that in 150 stomachs examined, corz.ercial or gDme fishes
oc- 
curred only a few times, as follows: Eel, once; grant, once; pickere!, twice;

trout, 9 times; sn-fishos, 10; yellow perch, 15; and catfish, 17 tines. A

more ccnsideration of these nurzbers would give azi impression adverse to
the 
bird, were it not for the fact that sunfishes are not of great value either

for food or sport,and catfishes are notorious spawn, eaters. That the great

blue heron undoubtedly eats scores of the enemy and competitor fishes for

every trout that it consumes is shown by the fact that va-ong such fishes
the 
following occurred in the stomachs mentioned: Suchers in 29, rin;ows in 23,

sticklebacks in 14, darters and carp in 7 erchi, idllifish in 5, cd sculpins,

gars, and madtoms in smaller numbers.