ABSTRACT
The syrinx is the organ responsible for producing the vast majority of bird sounds. Because its anatomyvaries greatly among bird taxa, prior knowledge of variations is extremely important to studies of functionalanatomy and phylogenetic systematics. With the aim of accessing and describing morphological variationin birds of the tribe Arini, this paper presents the findings of a comparative analysis of the syrinxes of 156specimens belonging to 47 species in 22 genera of the tribe. A number of hitherto unknown variationsare highlighted and confronted with the knowledge produced to date on the morphology of the syrinx inPsittaciformes. Some of the variations detected occurred in structures probably involved in sound productionand this should be taken into consideration in future studies of functional anatomy. Several characterssuggest the presence of a phylogenetic signal, given the congruence between their distribution among taxaand the hypotheses regarding monophyletic groupings proposed in the literature. Some of the variationsfound, including those suggesting a phylogenetic signal, are intraspecifically polymorphic, which reinforcesthe importance of using series of specimens in studies of syrinx anatomy.