•^■J Recejit Literature. lOQ 



general disposition; (i6) its value as food to man; (17) its furnishing 

 or not a habitat for troublesome parasitic entozoa; (18) its fecundity. 

 The discussion of these various points leaves one in no doubt whatever 

 that, whether or not the author has solved the problem, he has certainly 

 sketched many of its factors, and mapped out a proper course of study. 



Among "other considerations" with which the introduction continues 

 are : (i) the changing habits of birds ; (2) can they 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 fact 

 — e. g.. destruction, during the migration, of useful birds of prey); (5) 

 do birds of prey perform a necessary work by holding in check certain 

 birds and noxious animals.? (6) parasitism among birds; (7) the scien- 

 tific, educational and aesthetic 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. 



(J)) Birds which are known to be to some extent injurious, but whose 

 known services exceed their known 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, a, b, c.) 



Group III. Birds whose habits, so far as they are known, render them, 

 on the whole, injurious. 



(«) Birds whose known habits render them injurious at all times. 



(i5) 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 

 (^) — 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 moi'e 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 that we 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, showing 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. 



