MICE EATEN BY CROWS. 33 



MICE. 



Except when the ground is covered with snow, mice form one of the 

 more important articles of the Crow's food, ranking fourth in the list 

 of items of animal food. The average for the year almost equals that 

 of frogs and toads, and, with this exception, is exceeded only by insects 

 and by offal or carrion. The average for the year is little more than 1 

 percent (1.108 percent), but in March the amount reaches 3 J percent; 

 in April and May it exceeds 2 J percent, and though in June it falls 

 considerably below 1 percent (0.7 percent), it rises again to 2^ per 

 cent in July. But these averages, taken by themselves, would be rather 

 misleading, since they give little indication of the actual number of 

 mice killed or devoured. The highest average in the table occurs in 

 March; yet in that month only 3 stomachs out of 26, or less than 1 in 

 8, contained remains of mice, while in April 11 stomachs out of 42, or 

 more than 1 in 4, showed such remains, although the average quantity 

 in the latter month was only about two-thirds that in March. In May 

 47 Crows out of 364, or about 1 in 8, had eaten mice, while in July, 

 with approximately the same average amount, only 4 out of 45, or 1 

 in 11, contained their remains. 



A considerable number of the mice found in Crow stomachs should be 

 considered as carrion. In many cases the odor was sufficient to indicate 

 this fact; in other cases additional certainty was given by the presence 

 of carrion beetles or burying beetles (SiVphidce) of several species. In 

 many instances, however, these indications were useless, from the fact 

 that the remains of several different animals were present in the same 

 stomach, and it was impossible to connect the odor or the carrion bee- 

 tles more closely with one than another. 



It is probable that at least half the fragments of mice found in stom- 

 achs could be safely called carrion, but there is abundant proof from 

 several sources that Crows often capture living mice, particularly the 

 short-tailed meadow mice, which build their nests usually on the surface 

 of the ground, among the roots of grass. Here the Crows discover them, 

 and tearing the nest to pieces devour the young, and not infrequently 

 catch the adults as well. By far the greater number of the mice found 

 in the stomachs were meadow mice or voles (genus Microtus), and most 

 of them were the commonest species (Microtus pennsylvanicus). 



During the long winters of the Northern States, when snow covers 

 the earth continuously to a depth of several feet, these meadow mice 

 live in nests of dry grass on the surface of the ground, beneath the 

 snow. Dr. C. Hart Merriam states that in northern New York the 

 warmth of the nest and its contents causes the snow to melt around, 

 and especially above, the nest, forming a dome-shaped chamber in the 

 snow, which gradually increases in size until toward spring the snow 

 roof falls in or melts away, leaving a hole through which the grass nest 

 at the bottom may be seen. The Crows have learned to watch for these 

 3086-~No.6 3 



