Dear Julie,
Goosander and red-breasted merganser are have been found in many contexts
in swedish sites. They occur all the way from early postglacial sites
(sparse finds) up to historical periods. You should contact Per Eriscon in
the Natural History Museum in Stockholm. He keeps a data base on subfossil
bird finds in Sweden (nrm.se). In some sites from the viking age and early
medieval goosander and red-breasted merganser are very frequent. I have
investigated a find from the town Sigtuna (1000 AD.) where I found both
species. In the identification of the genus Merganser you can get some
help by looking at the work by Elisabeth Woelfle ("Vergleichend
morphologische Untersuchungen an Einzelknochen des postcranialen Skeletts
in Mitteleuropa vorkommender Enten, Halbgänze und Säger" published by the
university in Munich 1967).
There is one important character in the sternum of merganser that was
overlooked by Woelfle. On the dorsal side, just behind the articular
surfaces for the coracoids there is a pneumatic foramen. The area between
this foramen and the articular surfaces shows sexual dimorphism. I females
the area is flat or almost so, while in the males it is more heavily built
and convex. By this character you can sex the sternum and thus by the size
of the bone be confident in your species identification (male red-breasted
mergansers and female goosander overlap in size).
There in also a ossified structure that reaches a maximal development in
the males of these species. That is the syrinx that you find at the
bifurcation of the trachea. Males of many ducks have this special
development of the syrinx and my experience with bone collections in many
museums and deparments is that they often lack the syrinx in the male
ducks. It is easy to distinguish the goosander and the red-breasted
merganser. The syrinx of the former has a smooth surface while the other
has a granulated structure and is more strongly built. Even small pieces
of a syrinx is rather easy to distinguish once they are familiar to you.
In my analysis of the finds from Sigtuna I could demonstrate that there
was an even ratio of male/female among the red-breasted mergansers. Such a
condition was interpreted by me as fowling in the earle spring when these
birds migrate to their breeding localities. Once the females lay on their
eggs the males begin moulting and move to the open sea. Males and females
are also mixed during the winter, but I excluded the capture from that
season in this case because the Lake Mälar is ice-covered durin winter.
My results are unfortunately only published briefly (in swedish)but you
can get more information on request.
Good luck with your goosanders and look out for the syrinx.
Leif Jonsson
Laboratory of Archaeological Science (ANL)
Göteborg university
www.hum.gu.se/ark/ANL