Morphology of the basilar papilla of the budgerigar, Melopsittacus undulatus.

The budgerigar is a representative of the parrot-like birds that, like song birds, have developed complex communication signals. This species is interesting in a psychoacoustic sense, in that it shows unusually good frequency discriminative abilities above about 1 kHz. To begin to understand whether the peripheral hearing organ plays a role in such specializations, we have carried out a quantitative study of the fine anatomy of the basilar papilla and compared it to data from other avian species. The budgerigar basilar papilla is about 2.5 mm long in the living animal and contains about 5,400 hair cells. The hair cells of the papilla show regional specializations similar to those found in other birds and are described from scanning electron microscopic and light microscopic studies. Regiona changes in the basilar papilla, and in the basilar and tectorial membranes are described from light microscopic data. As noted for other avian species, the constellation of morphologic features found in the budgerigar is unique. In general, the hair cell patterns of the budgerigar papilla showed fewer specializations than found in, e.g., a songbird, the starling, but more than seen in a primitive land bird, e.g., the pigeon. There were no features that were obviously related to the unusal psychoacoustic performance of this species. © 1993 Wiley-Liss, Inc.