BirdAnalyst
Species · Illinois · BBS 2025 Release · 1966–2024

Summer Tanager Population Trend in Illinois

All statesGeneralists

Summer Tanager in Illinois has surged: up 29× on the route-weighted index since 1969.

29×Since 1969TrendPercent 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 →
55Routes In StateSurvey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
57YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Summer Tanager Trends in IllinoisNotable signalsLong-arc shifts the engine flags automatically — sustained declines or increases large enough to stand out from year-to-year noise.Full methodology →

long arc increasecomputed indexTrend sourceWhether the figure is our own computed route-weighted index or an official USGS modeled estimate. The current build labels every trend as computed.Full methodology →

Summer Tanager has surged in Illinois: up 29× on the route-weighted index since 1969.

Summer Tanager Population Forecast in Illinois

If the recent trend holds, Summer Tanager in Illinois is projected to stay roughly flat through 2029, near 1.4 (95% range 0.93–1.8). A 5-year backtest shows a typical error of ±21%, with 60% of held-out values landing inside the 95% band.

-6%Change 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 →
1.4Projected 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 →
0.93–1.895% 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 →
±21%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, Summer Tanager in Illinois is projected to stay roughly flat through 2029, near 1.4 (95% range 0.93–1.8). A 5-year backtest shows a typical error of ±21%, with 60% of held-out values landing inside the 95% band.19662029
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 →
20251.30.841.7
20261.30.861.7
20271.30.891.7
20281.30.911.8
20291.40.931.8

Summer Tanager Survey Routes in Illinois

Routes recording Summer Tanager in Illinois.
Recent countThe raw number of individuals recorded on this route in its most recent survey year. A single-route tally, not a trend.Full methodology →
Delwood1420241970
Sandusky1420231993
Beaverdam Lk1320231970
Cave In Rock1320241993
Belleview920241966
Bremen920241970
Karnak920242001
Pulaski820241971
Belknap720241970
Royalton620242001
Mascoutah Lk520241979
St Morgan420221969
Terre Haute320092009
Martinsville320121970
Mt Vernon320241975
Dudleyville320242001
Eldred320211993
York320242011
Grape Creek220242003
Eubanks220242008
Marshall220242010
Athens120242008
Atkinson120162016
Payson120182014
Clayton120232008

Summer Tanager Population Trend in Other States

alabamaarizonaarkansascaliforniadelawarefloridageorgiaindianaiowakansaskentuckylouisianamarylandmississippimissourinebraskanevadanew-jerseynew-mexiconorth-carolinaohiooklahomapennsylvaniasouth-carolinatennesseetexasutahvirginiawest-virginiawisconsin

Source: USGS North American Breeding Bird Survey, retrieved 2026-05-22.