On the coast, very abundant spring and autumn migrant, rare to uncommon in summer. Common summer visitant to the central and northern interior, where it is a widespread breeder. Nonbreeding The Bonaparte's Gull occurs throughout the province from sea level to at least 1,700 m elevation. On the coast, it frequents bays, harbours, lagoons, estuaries, areas of tidal convergence and upwelling, passages and narrows, as well as large rivers and sewage lagoons. Wherever food is abundant, concentrations of tens of thousands can occur.
Kelp beds, offshore islets, and log booms are favourite roosting sites.
In the interior, large lakes and rivers, estuaries, marshes, and ponds are preferred habitats. In spring, the Bonaparte's Gull is most numerous on the coast, especially in the vicinity of Pacific herring spawning areas in the Juan de Fuca Strait and Strait of Georgia, where flocks commonly number in the thousands. The northward movement usually begins in late March and early April. Numbers build throughout the month, peak in late April and early May, and begin to dwindle by mid-May. In late May, non-breeders begin to appear in numbers.