About 95% of the global Heermann’s Gull population breed on Isla Rasa, a tiny 142 acre Island in the Gulf of California. The nonbreeding range of this species is along the Pacific Coast from southern British Columbia to Guatamala (Islam and Velarde 2020).
Heermann’s Gull is accidental in Montana. The species was first detected in the state in 2018.
Direct Evidence of Breeding
Indirect Evidence of Breeding