BirdAnalyst
Species · BCR 34 · BBS 2025 Release · 1966–2024

Northern Beardless-Tyrannulet In Sierra Madre Occidental

All regionsSierra Madre OccidentalAerial insectivores

Northern Beardless-Tyrannulet in Sierra Madre Occidental has fallen sharply: down 67% on the route-weighted index since 1971.

-67%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 →
6Routes 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 →
49YearsYears 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 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 →

Northern Beardless-Tyrannulet has fallen sharply in Sierra Madre Occidental: down 67% on the route-weighted index since 1971.

Northern Beardless-Tyrannulet In Sierra Madre Occidental Population Forecast

If the recent trend holds, Northern Beardless-Tyrannulet in Sierra Madre Occidental is projected to fall about 49% by 2029 — from 0.28 in 2024 to a central estimate of 0.14 (95% range 0.00–0.49). A 5-year backtest shows a typical error of ±26.5%, with 100% of held-out values landing inside the 95% band.

-49%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 →
0.14Projected 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 →
0.00–0.4995% 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 →
±26.5%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, Northern Beardless-Tyrannulet in Sierra Madre Occidental is projected to fall about 49% by 2029 — from 0.28 in 2024 to a central estimate of 0.14 (95% range 0.00–0.49). A 5-year backtest shows a typical error of ±26.5%, with 100% of held-out values landing inside the 95% band.19692029
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 →
20250.160.000.51
20260.150.000.51
20270.150.000.50
20280.150.000.50
20290.140.000.49

Routes In Sierra Madre Occidental

Routes recording Northern Beardless-Tyrannulet in Sierra Madre Occidental.
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 →
PomereneARIZONA32024
SahuaritaARIZONA32019
Peña BlancaARIZONA12024
PatagoniaARIZONA12024
RedingtonARIZONA12021
AmadoARIZONA12022

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