AnimaliaHighest rank in taxonomy. Groups all life into domains: Animalia, Plantae, Fungi, etc.IUCN LCInternational Union for Conservation of Nature — the world authority on species extinction risk, using standardized criteria. — Least Concern — widespread and abundant; not at immediate risk of extinction.In ProgressCurrent stage of this record in the editorial review workflow. Recent Sighting
Chroicocephalus philadelphia
Bonaparte's Gull
(Ord, 1815)
Detailed Texts Multi-lang
One of the smallest gull species, characterized by its delicate, tern-like structure and fine, pointed black bill. In breeding plumage, adults exhibit a prominent slate-black hood, a white crescent around the rear of the eye, a pale grey back, and vibrant orange-red legs. In non-breeding winter plumage, the black hood is lost, replaced by a clean white head with a distinctive dark spot behind the eye, and the legs fade to pink. In flight, it is diagnosed by a striking, bright white triangle on the outer forewing, bordered by a thin black trailing edge on the wingtips.
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Anonymous Curator
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Under Review
Last modified by
Julia Trouin
TaxonomyBiological classification ranks placing this species within the tree of life, from Kingdom down to Genus.
PhylumRank below Kingdom. Groups organisms sharing a fundamental body plan (e.g., Chordata = vertebrates and some invertebrates).Chordata
ClassRank below Phylum. Subdivides by structural traits (e.g., Mammalia, Aves, Reptilia, Insecta).Aves
OrderRank below Class. Groups related families sharing common ancestry (e.g., Carnivora, Primates).Charadriiformes
FamilyRank below Order. Groups closely related genera (e.g., Felidae = cats, Canidae = dogs).Laridae
GenusRank just above Species. The first word in the two-part binomial scientific name.Chroicocephalus
Taxonomic AuthorityThe scientist who first formally described and published this species, followed by the year of publication.(Ord, 1815)
Record Completeness
96%Coming soon
Ecology & StatusHow this species lives: habitat preferences, diet, behavior, population status, and role in its ecosystem.
OriginWhether the species is native (evolved here), endemic (found only here), or introduced by human activity.
Native
Population TrendDirection of change in population size over time: increasing, stable, decreasing, or unknown.
Stable
Breeding SeasonTime of year when this species typically reproduces or flowers.
Year Round
Trophic RolePosition in the food chain: producer, herbivore, carnivore, omnivore, decomposer, or parasite.
Omnivore
Recent SightingsWhether this species has been observed in the wild in Costa Rica within recent years.
Yes
Habitat SummaryOverview of the specific ecosystems and environments where this species is found in Costa Rica. Multi-lang
Breeds across the interior boreal forest region of Canada and Alaska, specifically utilizing swampy openings, muskegs, and marshy edges of lakes and rivers bordered by coniferous trees. During migration and winter, it shifts to a wide variety of aquatic settings, including coastal bays, river estuaries, large lakes, sewage treatment ponds, and open ocean waters close to thermal fronts.BehaviourDaily activity patterns, movement, territory use, foraging style, and seasonal behavioral changes. Multi-lang
A highly migratory, diurnal bird that travels across the width of North America in loose flocks. They are agile aerial foragers that rely on keen vision to spot surface prey or flying insects. While breeding pairs can be fiercely territorial around their tree nesting sites, they transition into incredibly social, peaceful flocking dynamics on coastal wintering grounds.Social ActivitySocial structure: whether the species is solitary, paired, or colonial; hierarchy and communication. Multi-lang
Moderately social during the nesting season, forming loose, scattered colonies of 2 to 20 pairs within the same swampy tract. During the migratory and winter phases, their social behavior expands exponentially, forming expansive communal roosts and massive feeding flocks that readily mix with terns and other small gull species.Feeding GuildWhat the species eats, how it forages or hunts, and its role as a consumer in the food web. Multi-lang
Omnivore (seasonally insectivorous air-hawker and coastal surface-dipping piscivore/invertebrate generalist).Trophic Chain DetailsSpecific interactions in local food webs: prey species, predators, competitors, and scavengers. Multi-lang
Functions as a mid-level consumer in both terrestrial-boreal and coastal marine trophic webs. The opportunistically shifting diet relies heavily on flying and aquatic insects during summer, moving to small fish, krill, and marine invertebrates in winter. Eggs and chicks are preyed upon by ravens, crows, and raptors.Reproductive BehaviourMating strategies, courtship displays, nesting or spawning behavior, and parental care. Multi-lang
Monogamous for the season. Courting pairs engage in dramatic, loud, swooping aerial display flights. Uniquely, both sexes collect twigs, bark, moss, and lichens to build a sturdy, open-cup platform nest placed on a horizontal branch of a living conifer tree, up to 15 meters high. The female typically lays 2 to 3 buffy-green, darkly blotched eggs. Both parents actively share incubation duties for 22 to 24 days. The downy, semi-precocial chicks remain in the arboreal nest for about a week before leaving to follow parents to water.Physical Measures
Length (cm)
28.0 - 38.0 cm
Weight (Grams)
162 g - 270 g
Offspring per cycleTypical number of young (live births, eggs, or seeds) produced by one adult in a single reproductive event or breeding season.2 - 4
Sexual DimorphismObservable physical differences between males and females of the same species (e.g., size, coloration, features).Yes
Lifespan
Sexual MaturityAge at which the individual becomes capable of reproducing for the first time.
2 - 3 Years
Gestation / IncubationDuration from fertilization to birth (mammals) or to hatching (egg-laying species).
22 - 25
Lifespan EstimatedExpected duration of life from birth to natural death under wild conditions.
Males10 - 18 Years
Females10 - 18 Years
Sexual DimorphismPhysical differences in size, coloration, or morphology between males and females of this species.
Males Multi-lang
No plumage color differences. Displays subtle structural size dimorphism; adult males average marginally larger in wingspan, skeletal dimensions, and maintain a slightly heavier body weight than females.
Females Multi-lang
Shares the exact variable seasonal plumage morphs and black hood indicators, but structurally smaller in skeletal measurements and consistently lighter in overall body mass values.
Evolutionary AdaptationsInherited traits and behaviors that improve the species' survival and reproduction in its specific environment. Multi-lang
Exhibits specialized perching behavior and agile, flexible foot coordination that allows it to easily land and balance on thin branches of coniferous trees, an atypical nesting adaptation among larids.
Highly developed, buoyant, and lightweight aerodynamic design reminiscent of a tern, enabling rapid aerial hovering, banking, and sharp swoops to hawk flying insects directly out of the air during the summer months.
Main ThreatsDocumented pressures reducing the population: habitat loss, hunting, disease, climate change, and invasive species. Multi-lang
Vulnerable to logging and habitat fragmentation within the boreal forest zones, which eliminates mature conifers required for nesting. Climate change impacts, such as drying wetlands and altered insect emergence cycles, also threaten reproductive success.
Interesting FactsSurprising or notable facts that highlight what makes this species unique or ecologically important. Multi-lang
This species stands apart from nearly all other gulls by building small, tidy stick nests high up in trees (often up to 15 meters above ground) rather than relying on open scrapes on beaches or rocky shorelines.
Its vocalizations are entirely un-gull-like; instead of loud wails or laughs, it emits a low, raspy, nasal chattering call that sounds distinctly like a frog or a tern.