92 DISTRIBUTION IN NATURE IX 



As a result of these studies, certain regularities have emerged which are 

 briefly summarised in the following paragraphs : 



(i) Carotenoids in Feathers 



The colours of the feathers of birds, particularly of sub-tropical and tro- 

 pical birds, are often of extraordinary brilliance. Apart from basic blue and 

 white pigments and melanin pigments, various red and yellow lipochromes are 

 present, some of which possess carotenoid character. No example of the 

 isolation of a crystalline carotenoid from feathers seems to have been recorded 

 and the available information is wholly restricted to spectroscopic data. 

 Nevertheless it appears certain that bird feathers contain only phytoxanthins 

 (and their transformation products) , especially those with two hydroxyl groups 

 (xanthophyll, zeaxanthin, capsanthin^^) . 



By suitable feeding experiments Brockmann and Volker^^ showed that 

 canaries which have white feathers as a result of a xanthpphyll-free diet are 

 unable to absorb /^-carotene, lycopene or violaxanthin and to deposit these in 

 the feathers, even though the birds were in an otherwise healthy condition . The 

 feathers only assume their original yellow colour after feeding xanthophyll or 

 zeaxanthin. It was shown by Sauermann^" that paprica pigments are ad- 

 sorbed in the same way as xanthophyll and zeaxanthin and are deposited in 

 the feathers which, in this case, assume a red colouration. Examination of the 

 feathers of xanthophyll-fed birds showed that, apart from xanthophyll, a 

 transformation product of the latter was present, which has been termed 

 canaryxanthophyll (p. 337). In some birds yet another carotenoid, picofulvin, 

 has been found. The nature of canaryxanthophyll and picofulvin is not yet 

 known. The former is not identical with xanthophyll epoxide (p. 206) as might 

 be assumed in view of the similar absorption spectra (unpublished observation 

 by Karrer and Jucker). 



Apart from well-defined pigments such as xanthophyll and zeaxanthin and 

 pigments of unknown structure such as canaryxanthophyll and picofulvin, some 

 birds also contain carotenoids which appear to be related to astacene. Even these 

 more recent investigations are of a purely qualitative nature, while some of 

 the older observations, e.g. those of Krukenberg, are now only of historical 

 interest. Thus Krukenberg distinguished between 5 red and 5 yellow lipo- 

 chrome-type pigments. Of the red pigments, zoonerythrin^^ and rhodophan^^ 

 were most widely distributed. The behaviour of these two pigments is strongly 

 reminiscent of polyene pigments and their spectral properties and possible 

 combination with protein suggests a certain resemblance with astacene or 

 astaxanthin. The latest investigations by Lonnberg-^ and by Brockmann and 

 VoLKER confirm the probable relation to astacene. 



The nature of the yellow pigments mentioned by Krukenberg has been 

 References p. 108. 



