2 6 
Allen on Insectivorous Birds . 
in April it gains a credit of about twenty-two per cent. ; that in 
May, 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 u 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 sufficiently 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 “ the -probabilities seem to be against the Bluebird,” “ the 
certainties are, as yet, in its favor.” Taking into account, he 
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. 
