All About Birds has this to say about Bonaparte’s Gull:
A small, graceful gull with bright white patches in its wings, the Bonaparte’s Gull winters near people, but breeds in the isolated taiga and boreal forest (north of us in Canada)
The Bonaparte’s Gull is the only gull that regularly nests in trees.
The English name of the Bonaparte’s Gull honors Charles Lucien Bonaparte, who made important contributions to American ornithology while an active member of the Academy of Natural Sciences of Philadelphia during the 1820s. The scientific name philadelphia was given in 1815 by the describer of the species, George Ord of Philadelphia, presumably because he collected his specimen there.