This Grand Teton Black Yellow Bellied Marmot I photographed in Grand Teton National Park is actually a mutation of the more typical yellow bellied marmot. A melanistic population of yellow-bellied marmots have persisted in the Tetons for more than 80 years, with 15-23% of the population consisting of these “black marmots.” Development of the dark-colored pigment melanin in the fur is the opposite of albinism.