Problems with age-determination of seabirds due to heating of the corpses

The use of the bursa Fabricii as an indication of age in seabirds on dissection was discussed by Van Franeker (1983) and Hope Jones et al .(1982), The bursa is a sack-like organ, opening into the dorsal side of the cloaca and is more and more used as a character indicating immaturity. The bursa regresses completely in older birds. It is argued that also size (length and breadth) of this organ could be useful when estimating actual age. During Nay 1985 some 47 Guillemots Uria aalge were collected on the coast of Noord-Holland. All birds were covered with a layer of heavy oil, about 2 cm thick and, due to the sun and high temperatures at the time, were quite warm when collected. In fact they had absorbed heat for some days. Autopsy led to some confusing results, as compared to similar data on winter birds. A majority of the birds still had a bursa and could thus be determined as being immature. The size of the bursae however, was in general about 1.5x the biggest bursae ever found in winter collections.