April 20, 1900.] 



SCIENCE. 



629 



ond breeding season are certain to acquire fully 

 adult colors at the second postnuptial moult, if 

 they failed to do so at the iirst. 



Here then we have the facts about the Indigo 

 Bunting, and any specimen taken at the proper 

 time of year will verify them. Nevertheless, 

 Mr. Birtwell thinks that "for good results in 

 investigations upon color change one should 

 operate rather upon live birds in confinement. " 

 Well, perhaps so, for the ' proof of color change 

 without moult certainly does rest chiefly upon 

 caged birds. The fact that they moult irreg- 

 ularly and often at long intervals and, as for 

 instance in the case of the Purple Finch {Car- 

 podacus purpiireus), having once lost their bright 

 colors may never again regain them does not 

 seem to impair belief in a theory fifty years and 

 more old. It began when most people were 

 ignorant of the fact that birds could and did 

 moult twice in the year. This was sagely de- 

 clared to be too great a drain upon their vitality, 

 but when it was found that some species did 

 moult twice, theory had to be reserved for 

 others that did not appear to be guilty of drain- 

 ing their vitality. When these in turn were 

 proved to moult twice, refuge was taken in the 

 assumption that only certain individuals of 

 certain species changed color without moult. 

 Later came red-handed proofof guilt in feathers 

 found growing upon these individuals and the 

 believers in theory fell back upon the claim 

 that although one feather did seem to be re- 

 newed by moult, the one next to it underwent 

 a color change, concerning the nature of which 

 no two believers were agreed. Some of them 

 have gone so far as to assert rejuvenation of 

 frayed feather edges by some sort of exudative 

 processes which only need to be carried a step 

 farther to climate altogether the necessity of ■ 

 moult. This is no fancy picture and I only 

 paint it that my readers may know what 

 ' aptosochromatism' represents. 



Now, Mr. Birtwell comes forward with evi- 

 dence convincing him of the growth of new 

 feathers which expand of the wrong color and 

 then undergo a change to blue, at the same 

 time that the balance of old feathers also change. 

 He kept an Indigo Bunting in a cage and, wiser 

 than his predecessoi:s, who have seen caged 

 birds change color without loss of a feather, 



placed a ' fender ' about it, resulting in the cap- 

 ture of over 1300 cast-off or moulted feathers ! 

 He tells us that the change to the blue in the 

 new dull feathers had progressed ' excellently ' 

 when the bird died so that to this event he 

 evidently attaches no importance. I do, and 

 my opinion is that the dull feathers were defi- 

 cient in color as is frequently the case in caged 

 birds and never would have changed to blue 

 had the bird lived. The blue he saw was either 

 exposed by the wearing away of old feathers 

 originally blue, or it belonged to new feathers 

 the growth of which he failed to observe until 

 the feather sheaths were lost. It is extremely 

 easy to overlook growing body feathers which 

 may be small and take but a few days to de- 

 velop. The temptation is to make actual ex- 

 aminations of a struggling bird at long intervals 

 and see the rest of the changes we want to 

 through the bars of the cage, and I speak 

 from experience with several birds. An adult 

 male Indigo Bunting that I kept through the 

 winter and up to July lost practically no 

 feathers and yet members of my household were 

 confident he was changing to blue and so he 

 was by imperceptible loss of feather edgings. 

 His cage was in a bag of mosquito netting such 

 as I would commend to observers who cannot 

 find feathers while a bird ' changes color. ' 



Now, of course, all the theorizing and micro- 

 scopic evidence offered in Mr. Birtwell's article 

 is not of the slightest importance if his bird 

 did not do exactly what he claims it did, and I 

 have already indicated some of the possible 

 sources of error in observation. An observer 

 who did not know the plumage differences 

 between the adult and the young bird, nor 

 discover the structural differences between 

 autumnal and nuptial feathers, nor hesitate to 

 look for ' carrier pigment cells ' under the mi- 

 croscope, may well have his accuracy of obser- 

 vation questioned. These are some of the things 

 that do not tend to inspire us with confidence 

 in Mr. Birtwell's well-meaning and painstaking 

 article for the narrowness of his horizon prevents 

 facts being seen in their true light. It is so easy 

 to be mistaken, and a mountain of theory resting 

 upon a tiny and insecure base of alleged fact has 

 ere now brought the Chromatist to grief. When 

 the well-established laws of feather growth and 



