Fox Sparrow
Fox Sparrow has surged: up 680% on the route-weighted index since 1970.
About the Fox Sparrow
The Fox Sparrow (Passerella iliaca) is a North American member of the New World Sparrows (Passerellidae). In this analysis it is grouped with the forest birds.
- Size
- 4.5–7.5 in long (12–19 cm) — a small 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 479 Breeding Bird Survey routes across 11 states, most concentrated in the Northern Rockies.
- Family
- Passerellidae · Forest birds
Notable Fox Sparrow Trends
Fox Sparrow has surged in surveyed states: up 680% on the route-weighted index since 1970.
Fox Sparrow Population Forecast
If the recent trend holds, Fox Sparrow is projected to rise about 50% by 2029 — from 0.69 in 2024 to a central estimate of 1.0 (95% range 0.80–1.3). A 5-year backtest shows a typical error of ±48.8%, with 20% of held-out values landing inside the 95% band.
| Year | Projected index | 95% low | 95% high |
|---|---|---|---|
| 2025 | 0.98 | 0.74 | 1.2 |
| 2026 | 0.99 | 0.75 | 1.2 |
| 2027 | 1.0 | 0.77 | 1.2 |
| 2028 | 1.0 | 0.78 | 1.3 |
| 2029 | 1.0 | 0.80 | 1.3 |
Where the Fox Sparrow Is Detected
BBS routes recording Fox Sparrow, sized by most recent count.
Fox Sparrow Population Trend by State
| Alaska | +82% | 1975 | 128 |
| California | +233% | 1970 | 97 |
| Colorado | +395% | 1972 | 50 |
| Idaho | +365% | 1977 | 33 |
| Maine | +20% | 1995 | 11 |
| Montana | +232% | 1971 | 22 |
| Nevada | -4% | 1995 | 11 |
| Oregon | -66% | 1970 | 55 |
| Utah | -53% | 1979 | 21 |
| Washington | +10% | 1970 | 31 |
| Wyoming | -42% | 1970 | 20 |
Fox Sparrow Population Trend by Region
Bird Conservation Regions are the ecological unit for trends.
| BCR 2 | -32% | 1985 | 23 |
| BCR 3 | +145% | 1996 | 4 |
| BCR 4 | -38% | 1976 | 66 |
| Northern Pacific Rainforest | +71% | 1970 | 79 |
| Great Basin | +9% | 1970 | 72 |
| Northern Rockies | +43% | 1970 | 91 |
| Atlantic Northern Forest | -7% | 1995 | 11 |
| Sierra Nevada | +191% | 1970 | 38 |
| Southern Rockies / Colorado Plateau | +753% | 1972 | 66 |
| Coastal California | -83% | 1971 | 27 |
Fox Sparrow Conservation Status
Our route-weighted index shows it up about 680% since 1970.
Source: USGS North American Breeding Bird Survey, retrieved 2026-05-22. Trend is a route-weighted relative-abundance index, not an absolute population.