194 BULLETIN OF WISCONSIN NATURAL HISTORY SOCIETY. VOL. 2 NO. 4. 
shows the utter necessity of rearing the first brood as soon as 
possible. Furthermore, it is beheved that birds experience a phys- 
iological restlessness at the approach of the breeding season, as 
a result of which thev are led on to commence their migrations. 
(38.) 
Thus we have a sufficient explanation for the rapid northward 
movement in spring so often interpreted as showing a desire to 
be among the familiar haunts of the past season. 
Prof. W. K. Brooks, of Johns Hopkins University, presents 
us with an argument that is of quite another form. He holds 
with Prof. Baird that the main factors governing spring migra- 
tion are to be sought among the enemies to breeding (39). There 
is no doubt that birds nest where there is apt to be the least dan- 
ger from enemies. In fact, from the standpoint of natural selec- 
tion we should expect this. Areas with conditions destructive to 
bird life during the breeding season have always been known to 
be local, and it would be a questionable inference to say that the 
south as a whole, or even only generally, is dangerous to breed- 
ing birds. Yet this inference is necessary for the conclusions 
derived by Prof. Brooks, since we have migration occurring in a 
most orderly manner between the north and south as a wdiole, 
except in a few special cases. These will be treated separately. 
Prof. Brooks makes an analogy between the migrations of 
birds and those of fishes (40). An examination of the two phe- 
nomena will show that they are of quite a different order, and 
hence will permit of no just analogy\ The fishes referred to mi- 
grate regularly at the approach of the breeding season. In spite 
of many hardships they migrate inland from the ocean, often for 
several hundred miles, into the tributary streams. Here the food 
supply is far below the demand, and the question of food as an 
explanation fails. The eggs are deposited and left to the care of 
nature. Prof. Brooks probably makes his point that this migra- 
tion is purely a case of depositing eggs in some place safe from 
enemies. It is not, however, a movement into a fertile area, nor 
has it a general direction for the class. The course followed is 
one that will bring them to a desired local area. While fish mi- 
gration is thus a local phenomenon (if it is not Prof. Brooks does 
not give us such an impression), bird migration is a widespread 
38. Stated by Merriam in a lecture delivered at the U. S. Nat. Museum, 
Apr. 3, 1886. 
. 39. Brooks. Pop. Sc. Mo., vol. 52. p. 784. 
40. For my facts concerning the migration of fishes I am indebted to 
Prof. Brook's Article. 
