BirdAnalyst
Species · BCR 11 · BBS 2025 Release · 1966–2024

Forster's Tern In Prairie Potholes

All regionsPrairie PotholesWetland birds

Forster's Tern in Prairie Potholes has surged: up 302% on the route-weighted index since 1969.

+302%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 →
45Routes In RegionSurvey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
56YearsYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

Notable SignalsNotable 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 →

Forster's Tern has surged in Prairie Potholes: up 302% on the route-weighted index since 1969.

Forster's Tern In Prairie Potholes Population Forecast

If the recent trend holds, Forster's Tern in Prairie Potholes is projected to fall about 48% by 2029 — from 0.65 in 2024 to a central estimate of 0.34 (95% range 0.02–0.65). A 5-year backtest shows a typical error of ±81.5%, with 60% of held-out values landing inside the 95% band.

-48%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 →
0.34Projected 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 →
0.02–0.6595% 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 →
±81.5%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, Forster's Tern in Prairie Potholes is projected to fall about 48% by 2029 — from 0.65 in 2024 to a central estimate of 0.34 (95% range 0.02–0.65). A 5-year backtest shows a typical error of ±81.5%, with 60% of held-out values landing inside the 95% band.19672029
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 →
20250.320.000.63
20260.320.000.64
20270.330.010.64
20280.330.010.65
20290.340.020.65

Routes In Prairie Potholes

Routes recording Forster's Tern in Prairie Potholes.
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 →
Horsehead LkNORTH-DAKOTA442024
OkleeMINNESOTA71993
Lakota 2NORTH-DAKOTA42016
White LakeSOUTH-DAKOTA42011
Big StoneMINNESOTA32006
Lake GeorgeNORTH-DAKOTA32018
Long LakeSOUTH-DAKOTA32017
GluekMINNESOTA21988
ChokioMINNESOTA22004
GlyndonMINNESOTA22023
GryglaMINNESOTA22003
DanzigNORTH-DAKOTA22005
Danzig 2NORTH-DAKOTA22023
LennoxSOUTH-DAKOTA21981
Crow CreekSOUTH-DAKOTA22019
VeblenSOUTH-DAKOTA22008
BrittonSOUTH-DAKOTA22022
GettysburgSOUTH-DAKOTA22013
GarnerIOWA11986
TitonkaIOWA11981
ArlingtonMINNESOTA12004
CourtlandMINNESOTA12012
Redwood FallMINNESOTA11981
ErieMINNESOTA11984
BadgerMINNESOTA11998

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