How We Read The Survey

The Survey

The Breeding Bird Survey is a roadside count run since 1966. Each route is about 24.5 miles with 50 stops a half-mile apart, run once a year in June at dawn by a skilled volunteer doing three-minute point counts. About 3,000 routes run across the United States in a given year. We use standard-protocol runs only.

The Index We Compute

For each species, geography, and year we compute a route-weighted index: the total count divided by the number of routes that ran that year. It is a relative-abundance trend, not an absolute population. Long-term change compares a smoothed recent window to a smoothed baseline window.

Cite And Compute

USGS also publishes official modeled trend estimates with credible intervals. Our plan is to show both: the cited USGS figure alongside our own computed index, with a plain-English reconciliation. The current build labels every trend as computed; the cited layer is the next ingest.

Forecasts

We project the annual index forward with uncertainty bands and publish a backtest: we hold out the most recent years, forecast them, and report the error and how often the actual landed inside the band. A forecast is a projection of the current trend, not a prediction. Habitat, climate, and land use are not modeled.

What To Be Careful About

• Roadside bias: routes follow secondary roads and undersample roadless habitat.
• Observer effects: detection skill varies between observers and over time.
• Detectability: nocturnal birds, many waterbirds, and raptors are poorly sampled by point counts.
• Sparse series: we suppress trends and forecasts where the record is too short or thin.

Conservation Overlay

For wildlife trend data the conservation overlay is the legitimate, expected framing. We will surface USFWS Birds of Conservation Concern, Partners in Flight status, and state Species of Greatest Conservation Need, federal sources first. That ingest is the next milestone.

Sources

USGS North American Breeding Bird Survey, public domain (a work of the United States Government). We do not use eBird or other non-federal sightings data.