BirdAnalyst
Species · BBS 2025 Release · 1966–2024

Parasitic Jaeger

StercorariidaeSeabirdsStercorarius parasiticus

Parasitic Jaeger has fallen sharply: down 73% on the route-weighted index since 1985.

-73%Since 1985TrendPercent 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 →
20RoutesSurvey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
39Years 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 Parasitic Jaeger

The Parasitic Jaeger (Stercorarius parasiticus) is a North American member of the Skuas & Jaegers (Stercorariidae). In this analysis it is grouped with the seabirds.

Size
15.5–23.5 in long (40–60 cm) — a powerful seabird (typical for the family)
Habitat
Open ocean and coastlines, coming ashore mainly to nest in colonies.
Diet
Fish, squid and other marine animals caught at or below the surface.
Range
Recorded on 20 Breeding Bird Survey routes across 1 state, most concentrated in the BCR 2.
Family
Stercorariidae · Seabirds

Notable Parasitic Jaeger 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 Parasitic Jaeger. See the full index history below.

Parasitic Jaeger Population Forecast

If the recent trend holds, Parasitic Jaeger is projected to stay roughly flat through 2029, near 0.00 (95% range 0.00–0.00). A 5-year backtest shows a typical error of ±55.3%, 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 →
0.00–0.0095% 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 →
±55.3%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, Parasitic Jaeger is projected to stay roughly flat through 2029, near 0.00 (95% range 0.00–0.00). A 5-year backtest shows a typical error of ±55.3%, with 100% of held-out values landing inside the 95% band.19832029
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 →
20250.000.000.01
20260.000.000.01
20270.000.000.01
20280.000.000.01
20290.000.000.00

Where the Parasitic Jaeger Is Detected

BBS routes recording Parasitic Jaeger, sized by most recent count.

Parasitic Jaeger Population Trend by State

Parasitic Jaeger 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-88%198520

Parasitic Jaeger Population Trend by Region

Bird Conservation Regions are the ecological unit for trends.

Parasitic Jaeger 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 2-43%199113

Parasitic Jaeger Conservation Status

Our route-weighted index shows it down about 73% since 1985.

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