In spring, Tricolored Blackbirds stage one of California’s great birding spectacles, amassing in the tens of thousands to breed in the Central Valley. This season, the largest colony documented so far is in Merced County, with a preliminary estimate of 29,000 birds. Like many bird species, these charismatic blackbirds are extensively studied and monitored during the breeding season—after all, this is when they are most apparent across the landscape. Less is known about their lives during the rest of the year, when they disperse across the state and mingle with their more common cousins, like the Red-winged Blackbird. Insights from full annual-cycle tracking can expand our understanding and help guide conservation decision-making.
Protecting Colonies Takes Collaboration and Careful Timing
During the breeding season, we find tricolored blackbirds nesting in an array of habitats—upland grasslands, wetlands, and fallow fields. Many colonies, however, form in grain fields adjacent to dairies, in part because California has lost more than 90% of its historic wetland habitat, leaving fewer natural breeding sites across the landscape. Because these working lands are managed on tight seasonal timelines, nesting can create real challenges for both birds and producers.
Audubon has worked alongside partners at Natural Resources Conservation Service (NRCS), California Departments of Fish and Wildlife (CDFW), and the dairy industry to develop practical, collaborative solutions. Through targeted outreach and conservation incentives, we’ve protected the vast majority of colonies each year while minimizing financial impacts on dairy operators.
The success of our program has translated into an encouraging rebound in the population, up 58% between 2014 and 2025. Nevertheless, concerns remain about the long-term viability of the population, as agricultural practices and land uses change across their range. Water-use restrictions in the face of recurring drought may lead to extensive land retirement, which may translate into less nesting habitat in their core range. The rapid spread of utility-scale solar and urban development in the Central Valley and its fringes is already reducing both nesting and foraging habitat.
Advances in Technology Help Tricolored Blackbird Movements
In the face of these questions, there is a pressing need for more data on all aspects of the species’ habitat use. In 2025, Audubon California partnered with the California Department of Fish and Wildlife (CDFW) to tag breeding Tricolored Blackbirds with Cellular Tracking Technologies (CTT) Motus tags to generate novel understandings of their post-breeding and winter lives. We tagged 104 Tricolored Blackbirds and installed our fifth Motus station, complementing an already extensive network across California.
Avian tracking technologies are constantly advancing. Ultra-lightweight telemetry tags, including long-lasting battery and solar-powered options, now make it possible to track smaller birds and other wildlife than ever before. At the same time, robust receiver networks allow for autonomous data collection across broad geographic scales.
A Motus station is essentially an array of antennas connected to a computer that passively listens for distinctive coded signals at a specific radio frequency. When a tagged Tricolored Blackbird flies nearby (within 10 miles typically), its CTT Hybrid Tag emits a unique series of beeps every few seconds. The station logs these detections and every few days sends the data over the cellular network to Motus, where it is compiled in a massive, shared database.
Between May 2025 and April 2026, our 130 tagged birds were detected one million times! We’ve seen extensive movement of birds from the upper Sacramento Valley to the southern reaches of the San Joaquin Valley. Additionally, we’ve seen a few birds leave the Central Valley entirely, one to Monterey Bay and another crossing the Tehachapis heading south.
Tricolored Blackbirds Depend on Grasslands, Too
By late September 2025, 30 of the 104 Tricolored Blackbirds tagged at the time were detected at a single station in Solano County. We had built this station at Calhoun Cut Ecological Reserve because eBird Status and Trends predictions indicated the area was a major hotspot for post-breeding Tricolored Blackbirds. Sure enough, the Motus detections confirmed that a substantial number of individuals had congregated in this region, characterized by rolling hills of grazing land and irrigated pastures.
Though we often think of Tricolored Blackbirds as being associated with wetlands and dairies, this observation highlights the importance of grasslands to the birds’ habitat requirements.
Grasslands, among California’s most imperiled ecosystems with only around 1% of their historic range remaining, provide critical foraging resources for these blackbirds, as they are rich in nutritious invertebrates like grasshoppers. Their nesting colonies are rarely distant from pastures or rangelands, and our results indicate grassland habitats are also sought after in the fall.
Many insights remain unearthed from our Motus study, and we are only beginning to scratch the surface of the data. As our tagged birds progress through the 2026 breeding season, we are continuing to collect novel information about where they go after breeding and how they move between regions over the course of the year.
Already, cross-regional linkages are emerging between the Sacramento Valley and the Tulare Basin. Birds that bred in Colusa County last year were detected in Kern County this spring, where we anticipated they would breed in 2026. This Colusa County-to-Kern County connection is significant because it shows that Tricolored Blackbirds may be moving between major breeding regions, emphasizing the importance of protecting habitat across their broader range, not just at individual colony sites.
We are also partnering with other researchers studying the species in other regions. Ornithologists at Southern Sierra Research Station and the San Diego Natural History Museum have their own allotment of tags to affix to birds breeding in their respective regions.
Collectively, these data will help unlock a more cohesive picture of the species’ statewide, year-round distribution and habitat use.
This work is strengthened through collaboration with partners across the region:
- Fresno Audubon Society helped install the Motus station at Mendota, then went on to build their own tower at the Fresno Zoo, expanding the network’s reach in the Central Valley.
- Southern Sierra Research Station has provided extensive support with Motus installations and is also tagging Tricolored Blackbirds in the Kern River Valley, helping strengthen our understanding of the species’ movements across another important region.
- Point Blue Conservation Science supported the work through contractors who helped with the Mendota Motus station and assisted with some tagging efforts.
- The Nature Conservancy supported tagging efforts in the field.
- River Partners installed additional Motus towers in the region, which will help increase the chances of detecting tagged Tricolored Blackbirds as they move across the landscape.
Interested in future opportunities to get involved?
If you’d like to learn more about joining the next Tricolored Blackbird Triennial Survey in 2028, email Ian Souza-Cole at ian.souzacole@audubon.org.
