° 1912 ' J Recent Literature. 415 



beneficial, while we seldom hear it said or see it stated that an insect with 

 identically the same food material is beneficial. It is needless to say that 

 both the birds and the insects have the same economic importance." 

 (p. 309.) This point is very well taken, and brings us face to face with the 

 dilemma of rating many weevils as beneficial when they are certainly poten- 

 tially injurious and cases of the transfer of their attentions to cultivated 

 plants are not rare. It is a more practicable as well as more correct course 

 to follow Mason in rating them as well as the seed-eating birds as of neutral 

 significance. 



We are rather surprised to learn that Mason considers ants as of neutral 

 importance. They are far from so being in the American tropics, where 

 they are practically the " lords of creation." Even in the United States 

 we believe their bad qualities are preponderant. Mason differs decidedly 

 from American investigators regarding the value of the volumetric method 

 of estimating the contents of birds' stomachs, and we shall discuss this 

 important question at length elsewhere. 



Part IV of this report, a summary of the value of birds to agriculture 

 is of great interest, as being written by the eminent economic entomologist, 

 H. Maxwell-Lefroy. Some of his conclusions are as follows: 



" One has only to read the lists of the food of beneficial species to get an 

 idea of the immense part they play in reducing insect damage. Nearly 

 all insects have special enemies such as parasites which attack each indi- 

 vidually, but which produce alternative abundance and scarcity of each 

 insect; that is, with the natural action of the special checks such as para- 

 sites, you get alternate ' Waves ' of insect pest and parasite; this is where 

 the birds' importance is shown ; they are not restricted, they eat many kinds 

 of insects and when a pest has for the time got ahead and is abundant the 

 birds are there to feed on it just because it is abundant and because at one 

 time one is abundant, at another time another is, and the birds eat them all. 

 To put it figuratively they cut off the tops of the waves and tend to keep 

 them all at a uniform level, none being ever destructively abundant. In my 

 opinion from man's point of view this is the special function in nature of 

 birds and if the bird population is small outbreaks of insects are frequent." 

 (p. 364.) 



" The impression one gains by reading the detailed records and by 

 correlating it with one's knowledge of the insects is of a ceaseless war waged 

 by birds, not as a war but as the daily search for food, on edible insects 

 which are mainly those destructive ones which have a compensating very 

 high ratio of increase and which are ceaselessly breeding and increasing 

 against the ravages caused in their numbers by their enemies." (p. 368.) 



"It is difficult to overestimate the value of birds as a class and their 

 function seems to be, not so much the keeping down of individual destruc- 

 tive species (which is done by special parasites each destructive insect has), 

 as the cutting off of the crest of the wave of increase, the checking of those 

 insects which by favour of climatic or other influence elude their checks 

 and become abundant." (p. 369.) 



