Ars Magica query
Bjornaer, for the most part, view shapeshifting using other methods than the heartbeast as wrong.
Even other hermetic MuCo that allows them to change form.
In fact, they have a long-standing feud with a Gothic shapeshifter cult, who Birna (the founder) escaped from when she joined the order.
Best place to find more info is the Mystery Cults book, which goes into detail for Houses Bjornaer, Merinita, Criamon, and Verditius.