FEEDING HABITS 



193 



tents. Season to season, however, the actual amount of grit among New York grouse varies 

 but Httle. 



There is another difference attributable to food. Although exceptions are legion, there is 

 a tendency for gravel to be associated with food items which in themselves are not hard. 

 Conversely, less gravel is apt to be found mixed with such strongly protected seeds as cherry, 

 sumach and thornapple. The amount of gravel in the gizzard depends also upon what is avail- 

 able to the birds. In the rugged Adirondacks where the soils are predominantly sandy and 

 gravelly, grouse at all seasons of the year are likely to maintain in their gizzards nearly 

 twice as much gravel as do birds from the sedimentary clay or loam soils of the Catskills 

 or the Southern Tier (table 23). This difference is almost equally pronounced among the 

 grouse chicks whose first grinding material is picked up almost as soon as the first insect. 



TABLE 23. VOLUMETRIC PERCENTAGE OF GRAVEL IN THE GIZZARDS OF L093 ADULT 

 AND 510 CHICK GROUSE, FOR VARIOUS SEASONS OF THE YEAR 

 AND REGIONS OF THE STATE 



^Average for all seasons, adults: 12.2 per cent. 



The size of the gravel selected varies from half an inch in diameter down to fine particles, 

 the average being about one-eighth of an inch in thickness. Though all available colors are 

 chosen, white quartz pebbles seem to be picked up more often than would be accounted for 

 by random taking. Shape seems to be of little moment, as does also texture, for hard gran- 

 ites and soft shales are taken without apparent discrimination. 



Foods Often Considereb Injurious 



The grouse diet includes items which are known to be distasteful or actually poisonous to 

 many animal species. Judd"" early noted this, observing that, "The taste for rose hips, seedy 

 and husky as they are, and often beset with fine bristles which irritate the human skin and 

 would seem really dangerous to internal tissues, is one of the singular freaks of bird feed- 

 ing." It seems probable that spines and bristles must be wet and softened in the crop and 

 ground up in the gizzard, else the hard conical style-bases of avens (Geuiii) and fruits of 

 agrimony (Agrimonia) and the stiff spines of wild carrot ( Dauvus carola) and burdock 

 (Arctium) might prove difficuh to handle. At times these are taken extensively, a case in 

 point being a grouse from British Columbia, killed in October, in which Judd found 500 ap- 

 parently dead husks of Geum seeds. 



The ability of a bird to withstand the toxic effects of generally injurious plants can well 

 become an important factor in the survival of the species. Most of the poisonous species 

 utilized by grouse supply food in small amounts, but occasionally mountain laurel (Kalmia 

 lalijolia) is eaten in quantity. The harmful substance here involved is andromedotoxin, a 

 bitter glucosid which acts as a narcotic to many animals. Found in the leaves and in the 

 nectaries of the flowers, it is highly toxic to domestic livestock. Several fatalities from the 

 honey of this plant are on record. 



