236 FOOD HABITS AND REQUIREMENTS 



buds, all of which are staples for the rufled grouse in New York from November until April. 

 True, they eat much more in proportion to their size, for the normal contents of a grouse crop 

 in winter is almost as large in volume as is that of a pheasant, though the latter is usually twice 

 as heav\ . The abilitx to utilize buds for food is one reason uh\ the grouse ia:i sur\ive from 

 Alabama to Alaska. 



There are other ways in which food affects the existence of the species which arc much less 

 easy to identify, for there is much more to the study of food habits than the mere recognition 

 of the amount of each kind which is eaten. True, in analyzing the relation of food to health, 

 this is the first step. This done, the question naturalh arises as to the nutritive value of each 

 food to the bird. One can not logically assume that ati item commonlv eaten, bv that token, 

 must provide substantial nourishment. The next step, therefore, is to determine the amount 

 of each nutritive constituent — proteins, fats, carboh\drates and minerals — that are present in 

 the foods that constitute the normal diet. This can i)e accomplished by rather involved chem- 

 ical analyses. 



But all birds are not alike in their abilitv to break d<jwn tliese chemical constituents. To 

 complete the picture it is necessary, therefore, to conduct physiological tests, or "biological 

 assays" as they are known, bv which the degree to which grouse can utilize each important 

 food item can be determined. 



This chapter on foods deals largely with the first step in this sequence. Some progress, as 

 described shortl). has also been made on the second jjhasc. wherein the chemical composition 

 of a number of grouse foods has been determined. Hut the third phase, wilhuui which no 

 clear picture of the value of any individual food for grouse can be obtained, is more difficult 

 to study. With most mammals it is time-consuming, but otherwise not too didicult. to mea- 

 sure more or less accurately the amount of each nutrient which can be absorbed from an\ 

 given food. With birds, on the other hand, the carr\ ing out of such detailed biological as- 

 says, by chemically anahzing the feces, is complicated by the fact that the excretory prod- 

 ucts of the kidneys and the intestines cmpt\ into a conunon chamber, the cloaca. This 

 makes it im|)ossiblc to se|)arate the highl\ nitrogc-nous urates and ammonia from the rest of 

 the feces. In the delicate tests required these itenis can not be analysc-d together, thus making 

 it virtuallv impossible to attack the problem by this means. 



Because of the imporlanc c of ibis step, attempts lia\e been made to secure an index of 

 species digeslibilit\ \>\ othc-r less accurate methods. Variations in ihc- weight of grouse in 

 relation to the amount consumed of a single food item or of a combiiiatioTi of several kinds 

 have been cldcriiiined experimentally with hand-raised birds at the Research Center. A start 

 has also been made at testing the results of feeding grouse o\cr a considerable period of time 

 on one food by checking progressive changes in their ph\ siological reactions. 



The first of these methods yields results which arc at best onl\ indicative, while tlic second 

 invciKc's such liighU specialized ccpiipiiiciil and Ice linicpics as to make the completion of tests 

 bv it at best cxtrcmeh dilTicult. Nevertheless, the picture can not be complelc'd without such 

 analyses. Greater attention iherefore. must be concentrated on this phase of the problem. 



There arc also otlicT c|Mc>li(in> which luivc' a mcuc^ or less direct bearing on the relation of 

 grouse foods to licaitli. In the light of wlial is known, iiow does food aflect weight, reproduc- 

 tion and resistance to disease'.'' Is food one of the causes of periodic fluctuations in grouse 

 |)opulat ions'.'' Such indications of the answers as are available are hc-re presented, but the many 

 gaps ihal remain point lo tiiis licld as a parliciijarlv fniilfnl one fm future research. 



