^Upon examination of his bones in 2002, it was determined that Birger would have been just around 50 at the time of his death, about 10 years younger than previously believed. See Kari, Risto. Suomalaisten keskiaika. WSOY 2004. (ردمك 951-0-28321-5). See page 119.
^Prof. Jan Svanberg in Furstebilder från folkungatid (ردمك 91-85884-52-9) pp. 104-106
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