238 FOOD HABITS AND REQUIREMENTS 



is considerably more than the 21 per cent level considered satisfactory for domestic chicks, 

 but compares favorably with the 27 and 30 per cent that Psorris found were best suited to the 

 needs of young pheasant and quail respectively. 



The comparatively large protein requirements of grouse chicks decreases materially with 

 age. Those reared at the Research Center are now fed a ration containing 30 per cent pro- 

 tein, which is dropped to 20 per cent for adults*. 



It is suggested that the need for protein by chicks parallels closely the proportion of insects 

 found in the diet of wild birds. It has already been noted that insects make up about 70 per 

 cent of the total bulk of chick foods for the first two weeks following hatching. This ten- 

 dency rapidly falls off until by the end of August the food of young and adult are alike. 

 Most insects are relatively high in protein content. Carpenter ants, one of the most com- 

 monly eaten species, contain 30 per cent. 



Adults and older juveniles depend largely upon plant foods for their sustenance. .\s 

 regards protein content, the leaves of aspens, dandelions and clovers, and the buds of 

 cherries may stand them in good stead, for all are high in this respect as compared with 

 most other grouse food plants, though low by comparison with most insects. It should be 

 remembered, however, that digestibility varies with the kind of protein involved. As pre- 

 viously explained, biological assays are necessary to determine the ability of the grouse 

 to utilize the protein present in any given food. 



Fats 



These are considered so valuable a source of food that in dplcrniiniiig the nutritive ratio 

 they are gi\en a value two and a quarter time.~ that of carbohydrates. The crude fat, or ether 

 extract, given in chemical analyses represents the more or less digestible fats and oils as well 

 as the less easily broken down resins and waxes, chlorophyll and other substances soluble 

 in ether. 



Not all of the material here represented can be used by grouse. The crude fat content of 

 the ration fed to the birds at the Research Center is 5 per cent for juveniles and slightlv less 

 for adults. Even allowing for the indigestible fraction, a number of grouse foods contain 

 well above the ration standard. The buds of huj)-hornbeam stand out in this respect as do 

 leaves of mountain laurel. Surprisingly enough, hemlock needles and twigs, usually con- 

 sidered of little value as food, contain a large quantity of f;U. allhough niiuh of it is 

 probably in the form of resin. Sumach fruits are also high in fat content. 



Nitrogen-free Extract 



The term nitrogen-free extract is used to designate the more digestible carliohvdrates — 

 sugars, starches and other saccharides. Since these figures represent the remainder from the 

 other analyses rather than a separate analysis in themselves, small i|uuiililics of noii-car- 

 bohydrates, such as tannin, are unavoidably included. 



It is significant that the foods most commonly eaten by grouse are all wdlsiipplied with 

 these fat-producing and energy-releasing substances. The artificial ration led lo \ounu; birds 

 contains 40 per cent, which is raised to 53 per cent for the adults. Spring foods, with the 

 exception of hop-horn!)eam buds, together with all of the summer foods thus far analyzed 

 compare favorably with this standard. The high proportion of such carbohydrates in the 



* See Chapter XI. |>. 489 fur feeding schedules. 



