BIRDS IN RELATION TO AGRICULTURE 167 
Few people realize the extent to which birds feed upon 
and destroy insects. Certain species feed upon them wholly, 
others during part of the spring and summer seasons. 
Those birds that are partially insectivorous generally de- 
stroy large quantities of insects during the period of the 
year when they are raising their young broods, and this 
period coincides with the period of the year when insects are 
most prevalent. Certain families of birds diligently search 
the surface of the ground for insects, others search the vege- 
tation, and others the air, and in this manner the insects 
on the earth, under the earth, on the plants, and in the air 
are ceaselessly hunted (Plate XV). Investigations con- 
ducted on this continent and in Europe have shown the 
extent to which insects go to make up the diets of birds. 
For example, it has been found that insects constitute 65 
per cent of the total yearly food of woodpeckers, 96 per 
cent of that of flycatchers, 95 per cent of that of wrens, 
and 89 per cent of that of phcebes. Birds require an enor- 
mous amount of food when they are growing and, owing to 
their active habits, in the adult state. A young crow will 
daily consume twice its weight in food. Nash found that a 
young robin weighing three ounces would eat five and one- 
half ounces of cutworms in a day. It has been calculated 
that a pair of tits and the young they rear will consume about 
_ 170 pounds of insect food in a year. A blue tit will destroy 
six and one-half millions of insects in a year, and in bring- 
ing up a family of about twelve to sixteen young ones about 
24,000,000 insects would ultimately be accounted for. Grab, 
in Switzerland, states that three blue tits and three cole-tits 
consumed 8,000 to 9,000 insect eggs daily; three marsh-tits, 
one cole-tit, one long-tailed tit, and a golden-crested wren 
consumed 600 caterpillars in 100 minutes. Similar facts 
based on accurate observation and investigation might be 
quoted at great length to indicate the enormous destruction 
of insect life that is accomplished by birds. 
