Bonaparte’s Gull

Bonaparte’s Gull is the smallest gull to occur in New Hampshire, where it is primarily a spring and fall migrant along the coast. Smaller numbers occur in the winter, varying somewhat with temperatures and ice conditions to the north. Birds seen here in June or early July are likely late spring migrants or individuals (often immature birds) that did not return to their nesting areas in boreal Canada. During peak migration, a few Bonaparte’s Gulls also occur on inland lakes and rivers.

During the breeding season, Bonaparte’s Gulls are unusual in two respects: they are not strongly colonial and build their nests in trees. Nesting areas are typically in coniferous forest bordering lakes and ponds, where a given pond may support one to ten pairs, and even these are normally not close to one another. The nest is more substantial than those of ground-nesting gulls (all other species) and placed on a horizontal limb next to the trunk. Because of both these habits, plus their remote nesting areas, this species is less studied during the breeding season than most other gulls.

In contrast, it can be highly social during migration and winter, with flocks of thousands congregating in key staging areas during fall and early winter. As noted above, these groups shift around based on ice conditions, and there is some evidence that adults and young have different migratory strategies. Young birds are more common farther inland and may start migration earlier, while adults linger on large lakes while molting in late summer. At this time they start to lose their characteristic black head, and birds in New Hampshire in August can show a variety of plumages. Both adults and immatures are recognized in winter by the distinct dark patch behind the eye; the only other New Hampshire gull with a similar marking is the offshore Black-legged Kittiwake. Another useful identification feature in all plumages is the extensive white in the outer wing feathers when seen in flight.