10 CUCKOOS AND SHRIKES IN RELATION TO AGRICULTURE. 



still remains to be determined. As to the kinds of caterpillars eaten, 

 it may be said that the hairy and spiny species far outnumber the 

 smooth, but this may be due either to the greater abundance of the 

 hairy ones or to the bird's preference. 



This diet of hairy caterpillars has a curious effect upon the birds' 

 stomachs. A cuckoo's stomach, unlike that of seed-eating species, has 

 only a thin muscular coat on the outside, and the usual smooth lining 

 is almost entirely devoid of rugte or folds so characteristic of the 

 stomachs of many birds. This inuer layer is almost always found 

 pierced by at least a few caterpillar hairs ; often by so many as to be 

 completely furred and the membrane itself almost entirelj^ concealed. 

 Incidentally this hairy lining affords an excellent means of determining 

 the motion of the food during digestion. If a stomach is divided in the 

 plane of its two greater diameters the hairs on each half will be found 

 brushed around a center like the nap on the top of a silk hat, indicatiug 

 that the whole mass of food revolves in this ])lane. It may also be 

 noticed that the skins of caterpillars taken from the stomachs of birds 

 are always twisted like a cord or rope, and often require considerable 

 untwi.>ting before their characters can be determined. 



In a review of the food of cuckoos the most striking point is the 

 great number of (;aterpillars or lepidopterous larva^ which enter into 

 the year's diet. These insects are crude feeders, eating immense quan- 

 tities of vegetable tissue, and are usually so distended with it that the 

 amount of real nutrition in any one of them nuist be small. In fact, 

 stomachs of birds that have eaten largely of caterpillars always show 

 a quantity of this finely cut vegetable matter derived frcnn the insects' 

 stomachs. As digesticm 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, while the number of caterpillars found 

 in a stomach at any one time ])robably represents but a small i)ortion 

 of the actual daily consumption. From these consi«lerations it appears 

 that cuckoos must eat an enormous number of larv:e in the course of a 

 season. If the content:? of all the stomachs examined are regarded as 

 so many daily meals of the same bird, then the result indicates that 

 the bird has 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 in their 

 summer range; moreover, as indicated above, one cuckoo must eat sev- 

 eral meals a day, so this number (2,771) probably falls far short of 

 the actual number of caterpillars devoured by each cuckoo during the 

 season. 



In view of such considerations it seems hardly possible to overesti- 

 mate tlie value of the cuckoo's work. All cater[)illars are harmful, 

 many of them are pests, and any of them are likely to become so. The 

 common tent caterpillar formerly fed upon the wild cherry, but has 

 now turned its attention principally to apple trees, sometimes com- 



