SPECIALIZATIONS OF SOME CAROTENOID-BEARING FEATHERS STORRS L. OLSON Department of Pathobiology School of Hveiene_I and Public Health The Johns Hopkins University Baltimore, Maryland 21205 Certain of the Eurylaimidae (broadbills) the barb was composed of distinct light- and Cotingidae (cotingas) bear feathers of a colored cells. There was, however, a small violet or deep maroon color that is uncommon area of unorganized dark material at the in birds. These feathers show a number of larger end of the sections. Traced proximally peculiarities not found in typical feathers through serial sections, this dark area ex- colored by melanins or schemochromes (struc- panded until, in the region where barbules tural colors). I investigated the external and started to appear, it was discerned as the internal morphology of feathers from broad- medulla and was composed of distinct cells bills, cotingas, and other families in order to (fig. 1B). Further proximally, where the determine details of structure, amount of barbules reached their fullest development, variation between species, and the possible the medulla constituted an even larger area taxonomic value of these specialized feathers. (fig. 1C). The cortical cells, which were In a typical feather barb there are rows of quite distinct in distal sections, became dif- barbules present. Cross sections show two fuse and indistinguishable. A thick, wavy layers of cells: a prominent pigmented me- layer surrounding the outside of the barb, dulla surrounded by a cortex that usually in which no cells could be discerned, was appears clearer and more or less homo- particularly noticeable in the distal sections. geneous. Desselberger ( 1930) pointed out This layer, which was present in all the that when heavy deposits of lipochromes are feathers I examined, is what Strong (1952) present, barbs may be flattened, lack barbules, mistakenly alluded to as the cortex in QueruZu and be undifferentiated internally. Brush and purpurata. Strong (1902) earlier referred to Seifried (1968) showed a definite correlation the possible presence of an “epitrichium” (an between this modified structure and carote- inappropriate term for a feather component) noid deposition in the Gouldian Finch surrounding the barb cortex but regarded it (Poephilu gouldiue) and several other species. as purely an optical effect. That such is not the case is vividly demonstrated in Dryocopus METHODS pileatus (see below). Hereafter, for want of Feathers, obtained from museum skins, were selected a better term, I shall refer to this layer as the on the basis of their color and gloss. The gross cuticle. structure of barbs and barbules was examined micro- Guianan Cock-of-the-Rock. Rupicolu rupi- scopically. Feathers were embedded in nitrocellulose cokz. In the orange crown of males there is (Parlodion), following generally the methods out- lined in Galigher and Kozloff ( 1964). Paraffin was a subterminal band of deep brownish maroon not used as feathers embedded in it tended to shatter that illustrates particularly well the special- when cut. The entire feather was sectioned trans- izations associated with heavy depositions of versely on a rotary microtome from the distal carotenoids. Under magnification (fig. 2A), towards the proximal end. Sections were made at the orange portions of the barbs both proximal varying thicknesses,usually about 20 ~1. Unless other- wise stated, the descriptions were taken from the and distal to the maroon band were not ex- modified distal parts of the barbs. panded and bore barbules which were normal in size and number. However, on the maroon RESULTS band the barbs were flattened and the bar- COTINGIDAE bules, although still present, became vestigial. Sections through the maroon portion showed Red-ruffed Fruitcrow. Pyroderus scutatus. it to consist almost entirely of distinct cortical The throat and upper breast feathers are orange, tipped with a deeper scarlet-orange, cells, with only a few dispersed dark granules and they present a singular crinkled appear- of melanin indicating the location of the re- ance. The distal tips of the barbs lacked mains of the medulla (fig. 2B). In the orange barbules, were conspicously flattened, and it portions (either proximal or distal), the was here that the color was most intense. In medullar area increased in size and orga- distal sections (fig. 1A) the greater part of nization and the cortical cells became less The Condor, 72:424-430, 1970 14241 SPECIALIZATIONS OF SOME CAROTENOID-BEARING FEATHERS 425 m C b 6 C .. FIGURE 1. Cross sections from a barb of a throat feather of Pyroderus scututus. A. Section from modi- fied distal portion of barb. B. Section taken between A and C approximately where barb&s commence. C. Proximal section taken through area of well developed barbules. All sections are shown ventral side upper- most. m = medulla; c = cortex; b = barbule. distinct (fig. 2C), and in the region of normal ment of specialized carotenoid-containing barbule development, the medulla assumed feathers of any group of birds. Except for the its full stature and the outlines of the cortical remiges and rectrices, the males are adorned cells were lost (fig. 2D). entirely with glossy feathers ranging from Purple-throated Fruitcrow. Querula pur- deep maroon to blackish-purple. In the pumta. The maroon gorget feathers of the Pompadour Cotinga (X. punicea) the barbs male bear long, flattened, barbuleless barbs. were much elongated and lacked barbules There have been conflicting reports of the for at least two-thirds of their length. Distally, internal structure of these barbs. Strong the rachis itself was pigmented and became (1952) described cross sections as having a indistinguishable from the barbs, as at this thin outer layer surrounding a “homogeneous, point the branching became dichotomous, pigmented, central core . in which no trace rather than pinnate as is usual in most of medullary cells could be found,” whereas feathers. As in Querulu, there was no medulla Mattem (1956) reported cells in the pig- and the cortex revealed no definite cellular mented portions and large air-filled medullary structure. cells in proximal sections. She believed Cotinga. Males of this genus are bright Strongs’ observations resulted from fading blue, with patches of deep violet below. The of the pigments in the embedding medium he violet throat feathers from the Lovely Cotinga used, causing the cell outlines to become in- (C. amabilk) were glossy with flattened distinct. My observations confirm Strongs’ barbuleless barbs. Sections lacked a medulla; I could not distinguish cells in barbs of distinct cortical cells were present (fig. 3A). Querula (or Xipholena), nor did I find air- Some of the violet feathers, usually those of filled medullary cells. In a very few sections the belly, did not appear glossy and had there were scattered small, dark remnants of normal barbule development. In sections of medulla, such as illustrated in figure 2B for barbs from them (fig. 3B), a small medullar Rupicolu. The outer layer mentioned by spot was seen. This consisted of a dark area Strong represents the cuticle, the “core” being within a lighter area and contained no dis- the cortex. tinct cells. The cortical cells were apparent. Xiphokna. The three species of Xipholena Phoenicircus. Red crown feathers from exhibit perhaps the most extensive develop- males of the Guianan Red-Cotinga (P. carni- 426 STORRS L. OLSON A / I / / // / I / 1 ’ / / ’ 1 ’ / 1 ’ m m C b b C .6. FIGURE 2. A. Distal portion of a single barb from the crown of a male Rupicola rupicola; shaded portion is maroon, unshaded portions, orange. B-D. Cross sections of barb; dotted lines show approximate levels of the sections. All sections shown ventral side uppermost. m = medulla; c = cortex; b = barbule. fex) and the Black-necked Red-Cotinga (P. Red-banded Fruiteater. Pipreolu whitleyi. nigricollk) were examined. The distal barbs Feathers from the reddish-orange breast band lacked barbules; proximal barbs bore barbules of a male revealed flattened distal barbs with- at the base. No traces of a medulla were out barbules. There was a fairly large medul- found in P. nigricollis, while a few proximal lar spot at the larger end of the sections and sections of P. carnifex did show a dark central the cortical cells were in evidence. medullar vestige. Cortical cells were evident Purple-throated Cotinga. Porphyroluema in both species. porphyroluemu. Glossy, deep violet feathers FIGURE 3. A. Cross section of barb from glossy throat feather of Cotingu amabilis. B. Cross section of barb from non-glossy breast feather of Cotinga umubilis. C. Cross section of barb from cheek feather of Cymbirhynchus mucrorhynchus. D. Distal end of barb of cheek feather of Cymbirhynchus mucro- rhynchus. E. Cross section of barb from crown of Pipru uureokz. F. Cross section of barb from red feather of Phlogothruupis sunguinolentu. G. Cross section of barb from crest of Dryocopus pileutus. None to scale. All sections shown ventral side uppermost. m = medulla; c = cortex; b = barbule; cu = cuticle. SPECIALIZATIONS OF SOME CAROTENOID-BEARING FEATHERS 427 A m C D m C cu E F G 428‘ STORRS L. OLSON from the throat of a male bore flattened barbs THRAUPIDAE lacking barbules distally. Sections appeared Crimson-collared Tanager. Phlogothraupis more granular than in other species examined. sanguinolenta. The glossy red feathers of this A medullar spot could be found in only a species presented somewhat flattened barbs few sections, but cortical cells were distinct with at least rudimentary barbules through- in all. out their length. Cross sections revealed a PIPRIDAE definite dark medullar spot. Outlines of corti- cal cells could be distinguished only in the Crimson-hooded Manakin. Pipra aureola. pointed end of the sections (fig. 3F). Crimson crown feathers from a male bore barbs which were flattened distally and PICIDAE lacked barbules. Cross sections were elongate Pileated Woodpecker. Dyocopus pileatus. and pointed at one end. No medullar spot The glossy red crest feathers bear very long, was perceived; cortical cells were obvious barbuleless barbs, In section these presented (fig.