Dovekie: skull development and ageing

Dovekie or Little Auk Alle alle alle. Texel, The Netherlands
Culmen: 14.4 mm; total: 53.6 mm, unsexed adult

Skull

Skull development in Dovekies follows the same pattern as in Uria and Alca. During the first winter the separate bones of the juvenile skull fuse. This process will be more or less completed in spring of its second calendar year. By that time the development of the supraorbital ridge starts.
A fragile strip of bone is formed by the ossification of a ligament that runs above the eye between the the tip of the lachrimal bone towards the tip of the postorbital process and bony outcrops that are growing from the edge of the eyecase in between. These fragile bony structures meet each other during the second autumn and grow into a thin bony supraorbital ridge (sor) during its third calendar year. Between this ridge and the frontal bone a perforated depression, the fossa glandula nasalis, contains the crescent shaped salt gland. At the distal end of this depression a foramen is left allowing passage to a duct from the salt gland to the nasal cavitiy (Schmidt-Nielsen 1960).

The development of de supraorbital ridge provides an indication of age up to the third calendar year. After that the ridge becomes thicker and heavier with age. The robustness of the ridge might be a measure of age. Further research on this is needed.

Stages of skull development


Juvenile.First winter. Unsexed                                       Immature. Second winter. Unsexed

Subadult. Third winter. Unsexed                                    Subadult. Third winter. Unsexed

Adult. 4+ winter

All skulls are from birds collected on the Dutch and Belgian coast after the Tricolor oil spill in February 2003. Courtesey of Kees Camphuysen, NIOZ (Royal Netherlands Institute for Sea Research)

References