Bonaparte’s Gull, Chroicocephalus philadelphia

Bonaparte’s Gull, Chroicocephalus philadelphia. Photographs taken in the greater Los Cabos area of Baja California Sur, March 2017 and March 2018.

Bonaparte’s Gull, Chroicocephalus philadelphia. Photograph taken in the coastal area of Yavaros, Sonora, December 2016. Photograph and identification courtesy of David F Smith, Alamos, Sonora.

Background and Identification

Bonaparte’s Gull, Chroicocephalus philadelphia, is a member of the Laridae Family of Gulls, Terns and Skimmers. This species is monotypic, meaning that it is not divided into subspecies or smaller taxa and has a single member. Monotypic species show little variation in characteristics across their geographical range. Bonaparte’s Gull is one of the smallest gulls in North America and is often seen on beaches and coastal zones close to human activity. However, little is known about the breeding behavior of this species, as it breeds solitarily or in small colonies in remote habitats. In Mexico, Bonaparte’s Gull is known as Gaviota de Bonaparte.

At 28-38 cm in length, Bonaparte’s Gull is very small. Adults are typically monomorphic and both sexes exhibit distinct seasonal changes in plumage. During the breeding season, adult Bonaparte’s Gulls are characterized by their slender build, black heads, white underparts, and pale grey wings with black wingtips. During the non-breeding season, their heads become white with a small dark (grey or black) spot behind the eye. Year-round, they have a thin black bill, reddish legs, and a white tail.

Habitat and Geographical Range

Bonaparte’s Gulls are highly adaptable and can be found in a variety of habitats depending on the season. They are found on lakes, rivers, marshes, coastal bays and harbors, sandbars, mudflats, and beaches along coasts. They are opportunistic feeders eating a wide range of invertebrates and fish and limited amounts of insects. Nesting in trees is common, a unique behavior among North American Gulls.

The geographical range of the Bonaparte’s Gull includes breeding grounds in the northern parts of North America, from central Alaska across Canada to the Great Lakes region. In Mexico, they are winter visitors. During this time, they inhabit coastal regions in the Atlantic Slope from Tamaulipas to the northeast Yucatán Peninsula, in the central states of Chihuahua, Coahuila, and Nuevo León and within the Pacific Slope in Baja California and Baja California Sur and from Sonora to Nayarit at elevations up to 600 m (2,000 feet).

Common Misidentifications

Bonaparte’s Gull can be confused with other small gulls, particularly those with similar size and plumage patterns. One common look-alike is the Black-headed Gull, Chroicocephalus ridibundus, which also has a dark head during the breeding season but has a larger bill, a more rounded head, and a broader wing with more extensive black wingtips.

Conservation Status

From a conservation perspective Bonaparte’s Gull is currently considered to be of Least Concern with stable, widely distributed populations. Conservation efforts for Bonaparte’s Gull focus on protecting and managing their habitats, especially the boreal forest wetlands where they breed.