BirdAnalyst
Species · BBS 2025 Release · 1966–2024

Bonaparte's Gull

LaridaeWetland birdsChroicocephalus philadelphia

Bonaparte's Gull has declined: down 34% on the route-weighted index since 1982.

-34%Since 1982TrendPercent change in the route-weighted abundance index between a smoothed baseline window and the most recent one. It tracks direction, not absolute population.Full methodology →
62RoutesSurvey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
44Years SurveyedYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

About the Bonaparte's Gull

The Bonaparte's Gull (Chroicocephalus philadelphia) is a North American member of the Gulls, Terns & Skimmers (Laridae). In this analysis it is grouped with the wetland birds.

Size
8.5–31.5 in long (22–80 cm) — a long-winged waterbird (typical for the family)
Habitat
Marshes, ponds, lakeshores and other freshwater wetlands.
Diet
Aquatic invertebrates, small fish, frogs and plant matter.
Range
Recorded on 62 Breeding Bird Survey routes across 6 states, most concentrated in the BCR 4.
Family
Laridae · Wetland birds

Notable Bonaparte's Gull TrendsNotable signalsLong-arc shifts the engine flags automatically — sustained declines or increases large enough to stand out from year-to-year noise.Full methodology →

No notable trend signals for Bonaparte's Gull. See the full index history below.

Bonaparte's Gull Population Forecast

If the recent trend holds, Bonaparte's Gull is projected to stay roughly flat through 2029, near 0.00 (95% range 0.00–0.07). A 5-year backtest shows a typical error of ±241.2%, with 100% of held-out values landing inside the 95% band.

n/aChange by 2029TrendPercent change in the route-weighted abundance index between a smoothed baseline window and the most recent one. It tracks direction, not absolute population.Full methodology →
0.00Projected 2029 indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →
0.00–0.0795% range95% rangeThe 95% uncertainty band around the projection at the forecast horizon. The true value should land inside it most of the time.Full methodology →
±241.2%Backtest errorBacktest errorTypical error when we hold out the most recent years, forecast them, and compare to what actually happened. Lower means a more trustworthy projection.Full methodology →
If the recent trend holds, Bonaparte's Gull is projected to stay roughly flat through 2029, near 0.00 (95% range 0.00–0.07). A 5-year backtest shows a typical error of ±241.2%, with 100% of held-out values landing inside the 95% band.19712029
Projection of the recent trend (dashed) with 80/95% bands — a projection, not a prediction. Habitat, climate, and land use are not modeled.
YearProjected indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →95% low95% rangeThe 95% uncertainty band around the projection at the forecast horizon. The true value should land inside it most of the time.Full methodology →95% high95% rangeThe 95% uncertainty band around the projection at the forecast horizon. The true value should land inside it most of the time.Full methodology →
20250.000.000.07
20260.000.000.07
20270.000.000.07
20280.000.000.07
20290.000.000.07

Where the Bonaparte's Gull Is Detected

BBS routes recording Bonaparte's Gull, sized by most recent count.

Bonaparte's Gull Population Trend by State

Bonaparte's Gull population trend by state.
TrendPercent change in the route-weighted abundance index between a smoothed baseline window and the most recent one. It tracks direction, not absolute population.Full methodology →Baseline yearThe first year of the smoothed window the trend is measured from. An earlier baseline means a longer record stands behind the number.Full methodology →Survey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
Alaska-79%198453
Californiainsufficient datan/a4
Maineinsufficient datan/a1
North Dakotainsufficient datan/a1
Oregoninsufficient datan/a1
Washingtoninsufficient datan/a2

Bonaparte's Gull Population Trend by Region

Bird Conservation Regions are the ecological unit for trends.

Bonaparte's Gull population trend by Bird Conservation Region.
TrendPercent change in the route-weighted abundance index between a smoothed baseline window and the most recent one. It tracks direction, not absolute population.Full methodology →Baseline yearThe first year of the smoothed window the trend is measured from. An earlier baseline means a longer record stands behind the number.Full methodology →Survey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
BCR 2+37%19967
BCR 4-71%198433
Northern Pacific Rainforest+619%198418

Bonaparte's Gull Conservation Status

Our route-weighted index shows it down about 34% since 1982.

Source: USGS North American Breeding Bird Survey, retrieved 2026-05-22. Trend is a route-weighted relative-abundance index, not an absolute population.