120 Fretp Museum or Naturat History — Zoézocy, Vor. XI. 
conditions. Considering the great abundance of these animals in 
early days, we may well suppose that in poor “nut years”’ the scarcity 
of their favorite food would supply a sufficient cause; and assuming 
scarcity of food to be the dominant factor governing such concerted 
movements among these animals, the absence of such migrations at 
the present day may readily be explained on account of the enormous 
decrease in numbers of Squirrels and consequent abundance of nuts, 
even in poor years, for those that remain. 
Kennicott says, ‘‘After one of these grand migrations, very few of 
the ‘species are found in the localities from which they have moved, 
and these, as if alarmed at the unusual solitude, are silent and shy. 
They rapidly increase in numbers, however, and, in a few years, are as 
abundant as before. I am not aware that they ever migrate except 
when exceedingly abundant. Of these immense hordes, but few 
probably survive. No sudden increase in their numbers was heard of 
in southern Wisconsin after the several migrations from northern 
Illinois. Many are drowned in attempting to cross streams as has 
been stated; not a few are destroyed by man; some die from utter 
exhaustion; and, when forced to travel, in an unnatural manner, upon 
the ground, they fall an easy prey to rapacious birds and mammals, 
all of which feast when the squirrels migrate. I learn from Dr. Hoy, 
that one of these migrations is said to have taken place in southern 
Wisconsin in 1842; he witnessed another in 1847, and a third in 1852. 
From these facts, and from observations made in Ohio and elsewhere, 
he is of the opinion that the migrations, in most cases at least, occur 
at intervals of five years; and, if he be right, the squirrels, which are 
now exceedingly abundant again in southern Wisconsin, may be expected 
to migrate in the autumn of 1857.* He further says that the migra- 
tions observed by him in southern Wisconsin occurred when the mast 
was exceedingly abundant and the squirrels in excellent condition. 
Near Racine, they were observed passing southward in very large 
numbers for about two weeks, at the end of September and the begin- 
ning of October; and it was a month before all had passed. They 
moved along leisurely, stopping to feed in the fields, and upon the 
_ *It is interesting to note that Dr. Hoy’s prediction that Gray Squirrels would 
migrate in Wisconsin in 1857 was fulfilled. Inaletter to Mr. A. W. Brayton, written 
at Racine, April 2, 1878, he says, “Black and Gray Squirrels did migrate in 1857 as 
predicted. Whether there is a precise interval between these migrations I will not 
pretend to state, yet they did migrate in this section in 1847, 1852 and 1857, since 
which they have become so scarce that I could not determine whether there was an 
attempt to migrate or not, as they are nearly exterminated now in this vicinity. 
In 1857 I knew one negro who stood by a tree, in an open space on the line of a fence, 
and shot over twenty in one afternoon. In other years one might stand at the same 
place six months and not see one individual.’ (Brayton, Geol. Surv. Ohio, IV, 
1882, p. 111, foot note.) 
