Every spring, tens of thousands of Tricolored Blackbirds descend on California’s Central Valley in one of the state’s most dramatic wildlife spectacles. This year’s largest documented colony — roughly 29,000 birds in Merced County alone — draws birdwatchers and scientists in equal measure.
Yet for all that visibility, almost nothing was known about where these birds go once breeding season ends. A new radio-tagging study is beginning to change that. One million detections later, the data is already challenging what researchers thought they understood about the species’ habitat needs.
A spectacle hiding a mystery
The Tricolored Blackbird’s breeding season ranks among the most visible wildlife events in California. Nesting behavior has been well-studied precisely because the birds are impossible to miss — but once breeding ends, the picture goes dark. Until recently, scientists had little reliable data on where these birds travel, how far they range, or what habitats sustain them during the other nine months of the year.
Part of the challenge is habitat loss. California has shed more than 90% of its historic wetland habitat, pushing many colonies into grain fields near dairy operations and creating genuine tension with agricultural schedules. Audubon California has worked with the Natural Resources Conservation Service, CDFW, and the dairy industry to protect the majority of colonies each year while keeping disruption to producers manageable.
Those efforts have contributed to a meaningful recovery — the Tricolored Blackbird population rebounded 58% between 2014 and 2025. Long-term concerns remain. Drought-driven land retirement, rapid expansion of utility-scale solar, and urban growth are reshaping the Central Valley, and protecting a species under those pressures requires knowing far more than breeding-season data can provide.
Tagging a hundred birds and listening for a million signals
To fill that gap, Audubon California and CDFW launched a radio-tagging study in 2025. Researchers fitted 104 Tricolored Blackbirds with ultralight CTT Motus tags — small enough to carry without burdening the birds, yet durable enough to transmit for months.
The technology works through passive listening. A Motus station is an antenna array connected to a computer that monitors a specific radio frequency. When a tagged bird flies within roughly 10 miles, its tag emits a unique coded signal every few seconds, and the station logs each detection before periodically uploading the data to a shared continental database maintained by Motus.
Audubon installed its fifth California Motus station as part of this project. More stations mean fewer coverage gaps and more complete movement records. Between May 2025 and April 2026, the 104 tagged birds collectively generated one million detections — a figure that surprised the research team and opened a window into a part of the species’ life cycle that had been essentially invisible.
Grasslands, not just wetlands: a habitat surprise
One of the study’s earliest and most significant findings came in late September 2025, when 30 tagged birds converged on a single Motus station in Solano County, at Calhoun Cut Ecological Reserve. Researchers had placed that station there based on eBird predictions suggesting the area was a post-breeding hotspot. The data confirmed it.
What made the finding notable was the landscape itself. Calhoun Cut isn’t a wetland — it’s a rolling terrain of grazing land and irrigated pastures. Because Tricolored Blackbirds are widely associated with wetlands and dairy operations, the Solano County detections challenge that assumption directly.
California’s native grasslands rank among the most imperiled ecosystems in the state, with only about 1% of their historic range still intact. They offer rich invertebrate food sources, including grasshoppers, that support post-breeding recovery. If grasslands are critical fall habitat, conservation strategies focused solely on wetlands and breeding colonies are missing a substantial piece of the picture.
Birds crossing regions — and why that matters
The tracking data has also revealed the scale of Tricolored Blackbird movement across California. Birds tagged in the upper Sacramento Valley have turned up in the southern San Joaquin Valley. A few individuals went even farther — one reached Monterey Bay, another crossed the Tehachapi Mountains heading south.
These aren’t short-range movements. They suggest a species navigating the full length of the state in search of suitable habitat across seasons. The most consequential finding may involve cross-regional breeding connections: birds that nested in Colusa County in 2025 were later detected in Kern County in spring 2026, where researchers anticipated they would breed again.
That Colusa-to-Kern linkage indicates individual birds may shift between major breeding regions from year to year rather than remain loyal to a single colony site. This mobility changes the conservation calculus entirely. Protecting one colony or one patch of habitat isn’t sufficient — the birds’ survival depends on a connected network of suitable habitats spanning their full range.
What comes next for the tricolored tracking project
The study is still running. As tagged birds move through the 2026 breeding season, researchers continue collecting data on post-breeding dispersal and inter-regional movement. Ornithologists at the Southern Sierra Research Station and the San Diego Natural History Museum are now tagging birds in their own regions using the same Motus infrastructure, expanding the project’s geographic reach considerably.
When those datasets are combined, researchers expect to produce the first cohesive, year-round map of Tricolored Blackbird distribution and habitat use across California. That map will feed directly into practical decisions — which lands to prioritize for protection, where agricultural incentive programs can do the most good, how to allocate limited conservation resources as solar development and drought continue reshaping the Central Valley. For a species that was nearly invisible outside of breeding season just a few years ago, one million detections may be only the beginning.