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

Common Tern Population Trend in Wisconsin

All statesWetland birds

Common Tern in Wisconsin has collapsed: down 86% on the route-weighted index since 1969.

-86%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 →
3Routes 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 →
21YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable Common Tern Trends in WisconsinNotable 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 declinecomputed 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 →

Common Tern has collapsed in Wisconsin: down 86% on the route-weighted index since 1969.

Common Tern Population Forecast in Wisconsin

If the recent trend holds, Common Tern in Wisconsin is projected to fall about 100% by 2018 — from 0.15 in 2013 to a central estimate of 0.00 (95% range 0.00–0.89). A 5-year backtest shows a typical error of ±5116.5%, with 20% of held-out values landing inside the 95% band.

-100%Change by 2018TrendPercent 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 2018 indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →
0.00–0.8995% 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 →
±5116.5%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, Common Tern in Wisconsin is projected to fall about 100% by 2018 — from 0.15 in 2013 to a central estimate of 0.00 (95% range 0.00–0.89). A 5-year backtest shows a typical error of ±5116.5%, with 20% of held-out values landing inside the 95% band.19672018
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 →
20140.000.000.89
20150.000.000.89
20160.000.000.89
20170.000.000.89
20180.000.000.89

Common Tern Survey Routes in Wisconsin

Routes recording Common Tern in Wisconsin.
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 →
Washington I1320131967
Phillips420042004
Omro119801967

Common Tern Population Trend in Other States

alabamaalaskaconnecticutdelawarefloridaidahoindianalouisianamainemarylandmassachusettsmichiganminnesotamontananew-jerseynew-yorknorth-carolinanorth-dakotaohiorhode-islandsouth-dakotatexasvermontvirginiawashingtonwyoming

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