26 Allen on Insectivorous Birds. 



in April it gains a credit of about twenty-two per cent. ; that in 

 Mav, chiefly through the excess of predaceous beetles, this drops 

 to about six per cent. ; that in June it falls away to zero, and in July 

 to minus thirty per cent., thus just about wiping out the credits of 

 the previous months." The Hermit Thrush is counted a " public 

 enemy " on the score of his excessive destruction of predaceous 

 beetles. The Swainson's Thrush (under which name we in- 

 clude "the Alice Thrush ") has a better record and is regard- 

 ed as worthy of " what little encouragement and protection we 

 can give it during its brief stay." On the whole the Thrush 

 family, so far as our knowledge of their food extends, cannot be 

 awarded "any great economical value." 



Professor Forbes's showing for the •• beautiful and beloved" 

 Bluebird is certainly a surprise and a shock to our notions of its 

 innocence and hitherto supposed high degree of usefulness. His 

 detailed report.* based on an examination of eighty-six specimens, 

 shows that the species preys largely upon predaceous beetles and 

 ichneumons, the latter including special enemies of the cutworms 

 and grasshoppers. In view of the many uncertainties that enter 

 into the problem of the relation of carnivorous and parasitic 

 insects to those which form their natural prey — whether or not 

 their increase is sufticientlv rapid to keep up their due proportion 

 to these and also to furnish a surplus for destruction by birds — 

 Professor Forbes believes that (as he rather obscurely puts it) 

 while l " the probabilities seem to be against the Bluebird." " the 

 certainties are, as yet, in its favor." Taking into account, Re 

 adds in conclusion, '■' the certainty of the evil consequences of the 

 destruction of the Bluebird, and the uncertainty of the possible 

 good, I believe that, notwithstanding the apparent balance against 

 the species, even the most radical economist, the most indifferent 

 to the beauty and pleasure of the natural world, would have no 

 present justification for throttling the song of the Bluebird in his 

 garden with the hope of increasing thereby his annual store of 

 hay and cabbage." 



In respect to the general subject of the economic relation of 

 insectivorous birds to insects, and to the results already attained 

 through his detailed studies, Professor Forbes judiciously admits 

 that the observations thus far made are far too few to settle the ques- 

 tion, but that they indicate that the time has come for hesitation, 



* Amer. Entomol., new ser., Vol. I, pp. 215-218, 231-234, Sept. and Oct., 1880. 



