260 REPORT OF THE FOREST, FISH AND GAME COMMISSION. 



proves, that their diet consists for the most part of insects — very largely cater- 

 pillars — that are found in such places. 



An examination of 155 stomachs of the two species mentioned shows that 

 their food is practically all animal matter — that is, insects. Of this, nearly 

 one-half consists of caterpillars. These are eaten at all times, and stomachs taken 

 in every month of the cuckoos' stay on their northern range show a large per- 

 centage of these insects. Some pains were taken to ascertain the exact number 

 of caterpillars contained in the 155 stomachs, but as the process of digestion was fair 

 advanced in some cases, the result can only be considered as an approximation. 

 The number actually counted was 2,771, which were all found in 129 stomachs, the 

 other twenty-six being filled with other food. It is probable, and almost certain, 

 that 3,000 would be nearer the exact number. If the contents of all the stomachs 

 examined be regarded as so many daily meals of the same bird, then the result 

 indicates that the bird had eaten 2,771 caterpillars in 155 consecutive days, at 

 the rate of only one meal each day, and some days not eating any. Now 155 

 days is about the length of time that cuckoos remain on their summer range; 

 moreover, one cuckoo must eat several meals a day, so this number (2,771) probably 

 falls short of the actual number of caterpillars devoured by each cuckoo during the 

 season. From these considerations it appears that cuckoos must eat an enormous 

 number of larvae in the course of a summer. These insects are crude feeders, eating 

 immense quantities of vegetable tissue, and are usually so distended with it that 

 the amount of real nutrition contained in any one of them must be small. In 

 fact, stomachs of birds that have eaten largely of caterpillars always show a quantity 

 of this finely cut vegetable matter derived from the insects' stomachs. As 

 digestion in birds is rapid, it would seem necessary to fill the stomach several 

 times a day with such quickly digested and slightly nutritious food as this, so that 

 the number of caterpillars found in a stomach at any one time probably repre- 

 sents but a small portion of the actual daily consumption. As to the kinds of 

 caterpillars eaten by the cuckoos, it is a singular fact that the hairy and spiny 

 species far outnumber the smooth ones; this may be due either to the greater 

 abundance of the hairy ones or to the birds' preference. This disregard of hairs 

 or spines was well illustrated by one stomach which contained seven larvae of 

 the Io moth {Automeris io). These caterpillars are thickly studded along the 

 back and sides with tubercles from which grow many spines, that are not only 

 sharp but poisonous, and sting the hand quite severely when carelessly handled. 

 Several other stomachs contained a less number of these insects. 



Among the insects eaten by the cuckoos which are of economic interest to 

 forestry may be mentioned the tent caterpillar (Malacosoma), the fall webworm 



