. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. Relations of Cracid Genera • Vuillcumier Ahurrki aburri, but its display functions are not kno\\'n. 4) Attenuated Primaries Both sexes of Chamacpctcs iinicolor, C. goudotii, Ahurria oburii, Penelope pipile, and P. cumanensis have the two or three outer primaries attenuated. A similar modi- fication is also seen in Penelope argyrotis cohimbianiis, less so in P. supeiciliaris, and hardly at all in P. montagnii schferi. That such a modification is connected with sound production in a special fomi of flight display ("
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. Relations of Cracid Genera • Vuillcumier Ahurrki aburri, but its display functions are not kno\\'n. 4) Attenuated Primaries Both sexes of Chamacpctcs iinicolor, C. goudotii, Ahurria oburii, Penelope pipile, and P. cumanensis have the two or three outer primaries attenuated. A similar modi- fication is also seen in Penelope argyrotis cohimbianiis, less so in P. supeiciliaris, and hardly at all in P. montagnii schferi. That such a modification is connected with sound production in a special fomi of flight display ("drumming") is known definitely in F. cumanensis, and almost certain also for Chamaepetes and AbiiirUi. It is \'eiy interesting, however, that drumming flights have been reported in species which ha\'e nonnal outer primaries like Penelope piir- piiroscens (Sutton and Pettingill, 1942), and Penelopina nigra (Salvin and God- man, 1901). This suggests that attenuation serves to modify or amplify the sounds pro- duced with nonnal feathers. Although ac- curate voice descriptions are lacking for all species that have attenuated outer pri- maries, there may be some correlation, as suggested by the fact that there is no tracheal cur\'ature in Penelope pipile. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Harvard University. Museum of Comparative Zoology. Cambridge, Mass. : The Museum
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