Meeting Abstract

16.6  Sunday, Jan. 4  Syrinx of Northern Gannets (Morus bassanus): What are those lumps? MODRALL, J.T.*; KEATING, J.H.; MILLER, E.A.; POKRAS, M.A.; Tufts University, Grafton, MA; Tufts University, Grafton, MA; Tri-State Bird Rescue and Research, Newark, DE ; Tufts University, Grafton, MA jmodrall@verizon.net

The avian syrinx is located at the bifurcation of the trachea and is considered the vocal organ of birds. Variations in avian syringeal anatomy are vast and have been used for taxonomic purposes. However, scant documentation exists of the syringeal morphology and unusual syringeal appendages of Northern Gannets. They are sexually monomorphic, highly social, breed in dense colonies and use their voice for many purposes including pair bonding, individual recognition and territoriality. This study provides an anatomic and histologic description of the Northern Gannet syrinx and associated appendages. The gannet syrinx is tracheobronchial, with well developed tympana on the ventral and dorsal aspects, medial tympaniform membranes, pessulus and interbronchial ligament. The gannet syrinx is sparsely muscled. Most unusually, the gannet syrinx has bilateral appendages covering lateral tympaniform membranes (ltm), hereafter called syringeal nodules. The nodules span the ltm and adjacent interannular membranes, but are not attached to the ltm itself. The well vascularized nodules are composed mainly of adipocytes. They grow during development and appear to undergo atrophy during emaciation. Similarly sized nodules are present in both sexes. Nodule growth may explain vocal development of chicks. Given that the syrinx and associated membranes play a role in voice production, it is our hypothesis that syringeal nodules may modify vocal quality. Further, since these nodules change in size during maturation and with body condition, the nodules may provide a mechanism, or "truthful signal", by which gannets could assess the body condition or maturity of mates or competitors.