Circumstantial evidence is presented that suggests the Mourning Cloak undergoes regular seasonal up- and downslope movements in northern California. The species breeds at low elevations in spring and then disappears until autumn; its disappearance coincides with the appearance of fresh individuals in the Sierra Nevada alongside obvious hibernators.
Shapiro, Arthur M.
"Seasonal phenology and possible migration of the Mourning Cloak butterfly, Nymphalis antiopa (Lepidoptera: Nymphalidae) in California,"
Great Basin Naturalist: Vol. 46
, Article 8.
Available at: https://scholarsarchive.byu.edu/gbn/vol46/iss1/8