Bonaparte's gull (Larus philadelphia)

Description

Bonaparte's gull fact file

• Description
• Biology
• Range
• Habitat
• Status
• Threats
• Conservation
• Find out more
• Glossary
• References
• Print factsheet

Bonaparte's gull description

An unusually graceful, dove-like gull species, Bonaparte’s gull (Larus philadelphia) is one of the smallest gulls in North America. It is a striking bird, especially during the breeding season when the adult has a uniformly sooty-black ‘hood’ covering the face and crown, with contrasting white crescents around the eyes ⁽²⁾.

Bonaparte’s gull is light slate-grey on the shoulders, back and wings, and a distinct black line runs along the wing’s trailing edge ^{(2) (3) (4)}. The underparts and the tail are white ⁽²⁾, except for the grey neck and sides of the breast which merge with the grey upperparts ⁽⁴⁾. During the breeding season the breast may show a subtle rosy-pink tinge ⁽²⁾. This species has a black, spike-like bill which is longer and more slender in males than in females ^{(2) (3) (4)}. The legs are orange-red to pinkish ^{(2) (4)}.

During the non-breeding season, Bonaparte’s gull lacks the distinctive black hood. Instead, the head is entirely white, although it often has dark smudges on the top and in front of the eye, as well as a prominent, dark, isolated ear-spot behind the eye ^{(2) (3) (4)}. 

Juvenile Bonaparte’s gulls have a greyish-brown head and upperparts, often with a dark cap and ear-spot ⁽⁴⁾. The head may be partly mottled white during the summer ⁽²⁾. The wings of juvenile gulls are pale grey on the upperparts and have a prominent brownish-black bar across the wing, a narrow dark line around the wing tip, and strongly contrasting outer primaries. There is a narrow black band at the tip of the tail ⁽²⁾.

Although currently placed in the genus Larus, recent genetic and taxonomic studies have suggested that Bonaparte’s gull may in future be moved to the genus Chroicocephalus ^{(2) (5)}.

French

Mouette de Bonaparte.

Size

Length: 28 - 30 cm ⁽²⁾

Wingspan: 90 - 100 cm ⁽²⁾

Bonaparte's gull biology

Bonaparte’s gull is unusual among gulls in being one of the only species to nest primarily in trees, rather than on the ground. The breeding season in Alaska and Canada is short, lasting for only a few weeks between late May and early July ⁽²⁾. The male and female both contribute to the construction of the firm, cup-shaped nest, which is usually made out of twigs, small branches and tree bark, and lined with grasses, mosses and lichens. The nest is usually located up to four metres above the ground in a conifer species such as spruce ^{(2) (3)}, although nests have also been found on bent-over rushes and reeds around a metre above the water ⁽²⁾.

In general, the female will lay three eggs in the nest, although clutch size ranges between one and four. Both the male and female Bonaparte’s gull incubate the eggs for around 24 days, and once hatched, both adults will take turns to feed the young chicks until they fledge ^{(2) (3)}. Bonaparte’s gull remains on its breeding grounds until mid-July, when large flocks will gather for the southward migration ⁽²⁾.

During the breeding season, Bonaparte’s gull feeds mainly on insects which it catches mid-flight ⁽²⁾. Throughout the year this species will also forage for small fish, krill, insects, crustaceans, and other small invertebrates ^{(2) (6)}, usually gathering in large flocks to feed ^{(2) (3) (6)}. It typically employs a variety of foraging strategies to catch its prey ⁽³⁾, including plunge-diving from the air to seize prey from underwater, dipping for food from the surface during flight, sitting on the water and jabbing for prey as it passes ⁽²⁾, or picking up items while swimming or wading ⁽³⁾. It frequently feeds along tidal upwellings ⁽²⁾.

Bonaparte's gull range

Bonaparte’s gull is native to North America. It breeds in western Alaska and in Canada, from British Columbia east to Quebec ⁽⁶⁾.

This species spends the winter along the Pacific and Atlantic coasts of the United States, the Gulf Coast, Mexico and the Caribbean. Bonaparte’s gull also overwinters inland in the Great Lakes region and along major rivers ⁽²⁾.

Bonaparte's gull habitat

During the breeding season, Bonaparte’s gull inhabits remote wetland areas around ponds, bogs, bays, lakes, marshes and fiords, in the taiga and boreal forests of Alaska and Canada. It nests in trees close to water, usually in sparsely wooded habitats among conifers such as spruce or larch ^{(2) (6) (7)}.

Bonaparte’s gull winters in large flocks in coastal areas and around the Great Lakes ^{(2) (4) (6)}, usually on lakes, rivers, marshes, in bays and harbours, and on sandbars, mudflats and beaches ⁽²⁾.

Bonaparte's gull status

Bonaparte's gull is classified as Least Concern (LC) on the IUCN Red List ⁽¹⁾.

Bonaparte's gull threats

Although not currently considered threatened, Bonaparte’s gull is thought to be sensitive to human disturbance. The degradation of nesting habitat due to the construction of roads and other infrastructure is also a concern ⁽²⁾.

Bonaparte's gull conservation

There are currently no known conservation measures in place for Bonaparte’s gull, although it is afforded some protection by the Migratory Bird Treaty in North America ⁽²⁾.

This species is among the least studied gull species in North America due to its remote nesting habitat and relatively secretive breeding behaviours, and further research into all areas of its breeding biology, habitat ecology and physiology is therefore required. There are currently very few accurate population estimates for this enigmatic species, and determining the population size and its sensitivity to human disturbance and other potential threats would be extremely beneficial in informing any future conservation decisions ⁽²⁾.

Find out more

Find out more about Bonaparte’s gull and other birds:

• BirdLife International - Bonaparte’s gull:
  http://www.birdlife.org/datazone/speciesfactsheet.php?id=3242

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Glossary

Boreal forest

The sub-Arctic forest of the high northern latitudes that surrounds the North Pole and is mainly composed of coniferous trees.

Crustaceans

Diverse group of animals with jointed limbs and a hard external skeleton, characterised by the possession of two pairs of antennae, one pair of mandibles (mouthparts used for handling and processing food) and two pairs of maxillae (appendages used in eating, which are located behind the mandibles). Includes crabs, lobsters, shrimps, woodlice and barnacles.

Genus

A category used in taxonomy, which is below ‘family’ and above ‘species’. A genus tends to contain species that have characteristics in common. The genus forms the first part of a ‘binomial’ Latin species name; the second part is the specific name.

Incubate

To keep eggs warm so that development is possible.

Invertebrates

Animals with no backbone, such as insects, crustaceans, worms, molluscs, spiders, cnidarians (jellyfish, corals, sea anemones), echinoderms, and others.

Lichen

A composite organism made up of a fungus in a co-operative partnership with an alga. Owing to this partnership, lichens can thrive in harsh environments such as mountaintops and polar regions. Characteristically forms a crustlike or branching growth on rocks or tree trunks.

Primaries

The main flight feathers projecting along the outer edge of a bird’s wing.

Taiga

The sub-Arctic forest of the high northern latitudes that surrounds the pole and is mainly composed of coniferous trees.

Taxonomic

Relating to taxonomy, the science of classifying organisms, grouping together animals which share common features and are thought to have a common ancestor.

Upwelling

The upward movement of cold, nutrient-rich water from the ocean depths, usually as a result of winds and currents.

References

1. IUCN Red List (February, 2012)
   http://www.iucnredlist.org/
2. Burger, J. and Gochfeld, M. (2002) Bonaparte’s gull (Chroicocephalus philadelphia). In: Poole, A. (Ed.) The Birds of North America Online. Cornell Lab of Ornithology, Ithaca. Available at:
   http://bna.birds.cornell.edu/bna/species/634
3. Avibirds: European Birdguide Online - Bonaparte’s gull (February, 2012)
   http://www.avibirds.com/euhtml/Bonapartes_Gull.html
4. Olsen, K.M. (2004) Gulls of Europe, Asia and North America. Christopher Helm Publishers, London.
5. Banks, R.C., Chesser, R.T., Cicero, C., Dunn, J.L., Kratter, A.W., Lovette, I.J., Rasmussen, P.C., Remsen, J.V., Rising, J.D., Stotz, D.F. and Winker, K. (2008) Forty-ninth supplement to the American Ornithologists’ Union Check-list of North American Birds. The Auk, 125(3): 758-768.
6. BirdLife International (February, 2012)
   http://www.birdlife.org/
7. Waterbird Conservation for the Americas: Mid-Atlantic/New England/Maritimes Waterbird Conservation Plan - Bonaparte’s gull (February, 2012)
   http://www.fws.gov/birds/waterbirds/MANEM/PDFs/BOGU_final1.pdf