i8S3.] 
Recejit literature. 
109 
general disposition; (16) its value as food to man; (17) its furnishing 
01 not a habitat tor troublesome parasitic entozoa; (18) its fecundity. 
The discussion of these various points leaves one in no doubt whatever 
that, wbethel 01 not the author has solved the problem, he has certainly 
sketched many ot its factors, and mapped out a proper course of study. 
Among othei considerations” with which the introduction continues 
aie : (i) the changing habits of birds; (2) can thej' ever become abundant 
in thickly settled districts.? (3) what birds, if left to themselves, are likely 
to become most abundant as the country grows older.? (4) some birds may 
be injurious to a locality which they seldom or never visit (a curious foct 
destruction, during the migration, of useful birds of prey); (5) 
do birds of prey perform a necessary work by holding in check certain 
biids and noxious animals.? (6) parasitism among birds; (7) the scien¬ 
tific, educational and lesthetic value of birds. 
The Introduction closes with “a Temporary Classification of Wisconsin 
Birds on an economic basis,” as follows :— 
Group I. Birds whose habits, so far as they are known, render them, on 
the whole, beneficial. 
(«) Birds whose known habits render them beneficial at all times. 
( 3 ) Birds which are known to be to some extent injurious, but whose 
known services exceed tlieir knoAvn injuries. 
(c) Birds whose flesh is valuable for food, and whose present abundance 
and slight usefulness as insect destroyers make it proper to permit their 
destruction as game. 
Group II. Birds whose habits, so far as they are known, make it doubt¬ 
ful whether they are, on the whole, beneficial or injurious. (With three 
categories, «, b, c.) 
Group III. Birds whose habits, so far as they are known, render them, 
on the whole, injurious. 
(a) Birds whose known habits render them injurious at all times. 
(b) Birds which are known to be to some extent beneficial, but whose 
known injuries exceed their known services. 
It would certainly appear that most birds fall in group I, category (a) or 
{b) — happily for us and them ! 
A curious question is raised. How shall a bird’s food be expressed nu¬ 
merically in terms of debit and credit.? because neither relative volumes 
nor relative weights of beneficial or detrimental food-elements can express 
the true economic relations of the bird, any more than a peck of plums 
can be compared with a peck of curculios — any more than the destruction 
of 3000 phylloxera can be set against that of one coral-winged grass-hop¬ 
per. as it would be if bulk for bulk were gauged. The author’s method of 
meeting this difficulty, arising from the fact tliat Ave have no standard of 
insect values, is novel and ingenious, to say the least. It consists essen¬ 
tially in the use of heavy black lines of different lengths, shoAving graph¬ 
ically, not numerically, the ratios of animal or vegetal foods, of the several 
items of each, and particularly the ratios of “beneficial” and “detrimental’’ 
food-elements, and those undetermined in these respects. 
