BirdAnalyst
Species · BBS 2026 Release · 1966–2025

MacGillivray's Warbler Population Analysis

ParulidaeForest birdsGeothlypis tolmiei

MacGillivray's Warbler has surged: up 230% on the route-weighted index since 1970.

+230%Since 1970TrendPercent 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 →
624RoutesSurvey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
57Years SurveyedYears surveyedNumber of years with at least one standard-protocol run in this geography. A longer record makes the trend more reliable.Full methodology →

About the MacGillivray's Warbler

The MacGillivray's Warbler (Geothlypis tolmiei) is a North American member of the Wood-Warblers (Parulidae). In this analysis it is grouped with the forest birds.

Size
4.5–5.5 in long (11–14 cm) — a small, active songbird (typical for the family)
Habitat
Woodlands and forest edges, including wooded suburbs and parks.
Diet
Insects and spiders gleaned from foliage and bark, with seeds and berries in season.
Range
Recorded on 624 Breeding Bird Survey routes across 14 states, most concentrated in the Northern Rockies.
Family
Parulidae · Forest birds

Notable MacGillivray's Warbler TrendsNotable 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 →

MacGillivray's Warbler has surged in surveyed states: up 230% on the route-weighted index since 1970.

MacGillivray's Warbler Population Forecast

If the recent trend holds, MacGillivray's Warbler is projected to rise about 15% by 2030 — from 0.60 in 2025 to a central estimate of 0.69 (95% range 0.51–0.88). A 5-year backtest shows a typical error of ±45.4%, with 20% of held-out values landing inside the 95% band.

+15%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 →
0.69Projected 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 →
0.51–0.8895% 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 →
±45.4%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, MacGillivray's Warbler is projected to rise about 15% by 2030 — from 0.60 in 2025 to a central estimate of 0.69 (95% range 0.51–0.88). A 5-year backtest shows a typical error of ±45.4%, with 20% of held-out values landing inside the 95% band.19682030
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 →
20260.660.480.85
20270.670.480.85
20280.680.490.86
20290.680.500.87
20300.690.510.88

Where the MacGillivray's Warbler Is Detected

BBS routes recording MacGillivray's Warbler, sized by most recent count.

MacGillivray's Warbler Population Trend by State

MacGillivray's Warbler population trend by state.
TrendPercent 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 →Baseline yearThe first year of the smoothed window the trend is measured from. An earlier baseline means a longer record stands behind the number.Full methodology →Survey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
Alaska-93%198616
Arizonainsufficient datan/a4
California+241%1971114
Colorado+19%197081
Idaho+137%197347
Montana+95%197047
Nevada-55%199313
New Mexico-22%197014
Oregon-6%1970103
South Dakota+109%199310
Texasinsufficient datan/a1
Utah+398%197052
Washington-24%197079
Wyoming+164%197043

MacGillivray's Warbler Population Trend by Region

Bird Conservation Regions are the ecological unit for trends.

MacGillivray's Warbler population trend by Bird Conservation Region.
TrendPercent 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 →Baseline yearThe first year of the smoothed window the trend is measured from. An earlier baseline means a longer record stands behind the number.Full methodology →Survey routesHow many standard-protocol BBS routes contributed counts. More routes means a steadier, better-sampled index; very thin coverage is suppressed.Full methodology →
Northern Pacific Rainforest-47%1970132
Great Basin+27%1970109
Northern Rockies+72%1970153
Sierra Nevada-4%197236
Southern Rockies / Colorado Plateau+107%1970140
Badlands and Prairies+262%197817
Coastal California-45%197329
Sierra Madre Occidental+26%19984

MacGillivray's Warbler Conservation Status

Our route-weighted index shows it up about 230% since 1970.

Source: USGS North American Breeding Bird Survey, retrieved 2026-08-14. Trend is a route-weighted relative-abundance index, not an absolute population.