The diminutive form of the name, Ursula, was always more common than the root form, due to the popularity of the legend of St. Ursula and the 10,000 virgins.
Cite as: R. Le Get, J. Uckelman, S.L. Uckelman. "Ursa". In S.L. Uckelman, ed. The Dictionary of Medieval Names from European Sources, Edition 2015, no. 2. http://dmnes.org/2015/2/name/Ursa.