BirdAnalyst
Species · BCR 37 · BBS 2026 Release · 1966–2025

Gull-billed Tern In Gulf Coastal Prairie

All regionsGulf Coastal PrairieWetland birds

Gull-billed Tern in Gulf Coastal Prairie has risen sharply: up 51% on the route-weighted index since 1971.

+51%Since 1971TrendPercent 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 →
20Routes 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 →
51YearsYears 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 →

Gull-billed Tern has risen sharply in Gulf Coastal Prairie: up 51% on the route-weighted index since 1971.

Gull-billed Tern In Gulf Coastal Prairie Population Forecast

If the recent trend holds, Gull-billed Tern in Gulf Coastal Prairie is projected to rise about 119% by 2030 — from 0.64 in 2025 to a central estimate of 1.4 (95% range 0.00–3.3). A 5-year backtest shows a typical error of ±312.5%, with 100% of held-out values landing inside the 95% band.

+119%Change by 2030TrendPercent 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 2030 indexProjected indexThe central forecast of the abundance index if the recent trend continues. A projection of the current trajectory, not a prediction.Full methodology →
0.00–3.395% 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 →
±312.5%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, Gull-billed Tern in Gulf Coastal Prairie is projected to rise about 119% by 2030 — from 0.64 in 2025 to a central estimate of 1.4 (95% range 0.00–3.3). A 5-year backtest shows a typical error of ±312.5%, with 100% of held-out values landing inside the 95% band.19672030
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 →
20261.40.003.3
20271.40.003.3
20281.40.003.3
20291.40.003.3
20301.40.003.3

Routes In Gulf Coastal Prairie

Routes recording Gull-billed Tern in Gulf Coastal Prairie.
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 →
Loyola BeachTEXAS162007
Bayside 3TEXAS102025
BaysideTEXAS72010
Lag AtascosaTEXAS32018
IndianolaTEXAS32024
WinnieTEXAS32025
Grand IsleLOUISIANA22014
Sabine NwrLOUISIANA21996
PetronilaTEXAS21999
ChinquapinTEXAS22011
Oyster LakeTEXAS22021
Loyola Beach 2TEXAS22011
Bayside 2TEXAS22004
Gran ChenierLOUISIANA11971
Forked IslandLOUISIANA12024
VanderbiltTEXAS11970
StowellTEXAS12010
DanburyTEXAS12012
L. Atascosa NwrTEXAS12025
Padre Island PaisTEXAS12015

Source: USGS North American Breeding Bird Survey, retrieved 2026-08-14.