Functional Morphology and Adaptive Significance of the Jaw Apparatus of the Parakeet Auklet (Aethia psittacula, Alcidae)

Abstract

The jaw apparatus of the parakeet auklet (Aethia psittacula) has been investigated in comparison to that of the crested auklet (Aethia cristatella). The mechanical and biological effects of the distinctive bill structure in the parakeet auklet have been analyzed. The oral slit is concave; therefore, equilibrium is achieved without the need for disabling the posterior or anterior parts of the dorsal adductor of the lower jaw and the adductor can act with the maximal force regardless of the position of the object clamped in the bill. Shearing of large food objects, such as polychaetes and jellyfish, by the parakeet auklet bill is a jaw apparatus specialization unique among birds. Strengthening of the jaw apparatus, which was initially adapted for capturing small planktonic crustaceans, involved the development of additional aponeuroses in the internal adductor, consolidation of the latter, shortening of the bill, and changes of the shape of the oral slit opening.