Trost, Charles H. 1999. “Black-billed Magpie (Pica hudsonia).” The Birds of North America, edited by Paul G. Rodewald. Ithaca: Cornell Lab of Ornithology. Retrieved from the Birds of North America: https://birdsna.org/Species-Account/bna/species/bkbmag1 doi: 10.2173/bna.389