A bird that changes colour without moulting: how the wîskicâhk (Canada Jay, Perisoreus canadensis) tricked the taxonomists

Abstract

Avian and mammalian colours are thought to be constant in life and in museum specimens, but several early 20th-century taxonomists singled out the Canada Jay (Perisoreus canadensis (Linnaeus, 1766)) as having unstable feather pigments and warned against using old museum specimens for taxonomic purposes. One such error was Brisson’s (1760) original naming of the species as “the Brown Jay of Canada”. Another was Ridgway’s (1899) naming of the “Gray Jay” as a new subspecies, Perisoreus (canadensis) griseus, through inappropriate comparison of fresh grey specimens with old brown ones. We discovered that browning of initially grey plumage also occurs between annual moults in living individuals of the Canada Jay’s Pacific morphotype. We documented this change using photographs and re-sightings of colour-banded individuals and through spectral analysis of year-old (brown) and incoming (grey) rectrices collected from the same moulting individuals. To assess the distribution of this colour change, we compared September vs. May eBird photographs from across North America. We showed that seasonal colour change is normal in the Pacific morphotype but rare in the two other morphotypes. Collectively, these data have important implications for the taxonomy of the Canada Jay and are a cautionary tale for taxonomists studying animal colouration.