264 USEFUL BIRDS. 
cow, cow, repeated monotonously many times, and sometimes 
preceded by a short chuckle. The bird often calls at night, 
and toward autumn its notes may sometimes be heard in the 
air as it passes overhead, probably in migration. Usually 
when the bird is heard at 
night in the spring and early 
summer it appears to be 
stationary. There is some 
»mystery in the wakefulness and 
night flight of Cuckoos, for they are 
certainly as wide-awake at times as the 
pet a ee Owl or Whip-poor-will at night, and often 
billed Cuckoo, one. seem slow and sleepy by day. 
ae The Cuckoos are of the greatest service 
to the farmer, by reason of their well-known fondness for 
caterpillars, particularly the hairy species. No caterpillars 
are safe from the Cuckoo. It does not matter how hairy or 
spiny they are, or how well they 
may be protected by webs. Often 
the stomach of the Cuckoo will be 
found lined with a felted mass of 
caterpillar hairs, and sometimes ig. 120.— Caterpillar of the Io 
its intestines are pierced by the ee 
spines of the noxious caterpillars that it has swallowed. 
Wherever caterpillar outbreaks occur we hear the calls of 
the Cuckoos. There they stay; there they bring their 
newly fledged young; and the number of caterpillars they 
eat is incredible. Professor Beal states that two thousand, 
seven hundred and seventy-one 
caterpillars were found in the 
stomachs of one hundred and 
twenty-one Cuckoos, —an aver- 
Fig. 121.—Spiny elm caterpillar. aoe of more than twenty-one each. 
Dr. Otto Lugger found several hundred small hairy cater- 
pillars in the stomach of a single bird. The poisonous, 
spined caterpillars of the Io moth, the almost equally dis- 
agreeable caterpillars of the brown-tail moth, and the spiny 
elm caterpillar, are eaten with avidity. 
While the above statements may apply to either of our 
