How Tiny Motus Tags Reveal Winter Journeys of American Kestrels in California | Exotic Nest

Wintering Kestrels Around the Salton Sea

The Salton Sea region of Southern California serves as a vital refuge for a wide array of migratory birds, including the diminutive American Kestrel (Falco sparverius). During the non‑breeding months these falcons patrol field margins, irrigation ditches, and open scrub, hunting insects and small vertebrates. Because the area lies on the Pacific Flyway, it supports roughly two hundred bird species and provides essential foraging and roosting opportunities for raptors that must survive the colder season.

Why Track Kestrels in Winter?

Population surveys have shown a steady decline in American Kestrels across much of their range. Researchers suspect that conditions encountered during the winter months—such as food availability, habitat quality, and exposure to pesticides—play a significant role in survival and subsequent breeding success. Understanding where individual birds spend their winter, how far they travel, and which habitats they favor is therefore a cornerstone of any conservation strategy.

Motus Technology: Small Tags, Big Data

In early 2026 a team of biologists, led by conservation scientist Teresa Ely, deployed a set of lightweight radio transmitters compatible with the continental Motus Wildlife Tracking Network. Each device weighs less than a gram, making it suitable for a bird that averages only 100‑120 grams in body mass. The tags emit a brief signal at regular intervals; when a tagged kestrel flies within range of a Motus receiver, the station records a “ping” that includes the bird’s unique identifier, time stamp, and geographic coordinates.

Twenty kestrels were captured using standard raptor banding techniques, fitted with the transmitters, and released at several sites surrounding the Salton Sea. The birds were then monitored by an array of receivers positioned at wildlife refuges, agricultural stations, and along major roadways. Over the course of the winter, each detection added a data point to a growing map of individual movements.

Key Findings From the First Winter

• Range of movement: Several birds were recorded traveling more than 150 kilometers between successive detections, indicating that kestrels readily use a mosaic of habitats rather than remaining confined to a single field.
• Habitat preference: The majority of pings originated near irrigated cropland and riparian corridors, suggesting these features provide reliable prey during colder months.
• Site fidelity: A subset of individuals returned to the same detection zone on multiple nights, hinting at short‑term territory establishment even in a non‑breeding context.
• Timing of departure: The earliest outbound movements were logged in late February, aligning with the onset of spring migration for many Pacific Flyway species.

These observations, while preliminary, illustrate how a network of tiny receivers can transform an otherwise invisible winter routine into a traceable pattern. The data also highlight the importance of maintaining agricultural edge habitats and water‑linked corridors in the Salton Sea basin.

Learning Opportunities for Volunteers

During the field season, the project welcomed undergraduate students and citizen‑science volunteers. Participants received hands‑on training in safe raptor handling, banding protocols, and the ethical attachment of transmitters. By involving emerging biologists, the team not only expanded its capacity for data collection but also fostered a new generation of advocates for raptor conservation.

Connecting the Full Annual Cycle

The Motus detections are being integrated with traditional banding records, nest‑box monitoring, and satellite observations of migration routes. This holistic approach aims to map the entire life cycle of the American Kestrel in California—from breeding territories in the Sierra Nevada, through migratory stopovers, to wintering grounds around the Salton Sea. Such comprehensive knowledge is essential for designing land‑use policies that protect critical habitats year‑round.

Future Directions

1. Expand the receiver network to include additional agricultural valleys and desert washes, improving detection coverage.
2. Increase sample size by tagging more individuals across different age classes to assess whether juveniles exhibit distinct winter behaviors.
3. Collaborate with local growers to implement kestrel‑friendly practices, such as reduced pesticide use and preservation of field margins.
4. Publish detailed movement analyses in peer‑reviewed journals to inform regional wildlife management plans.

By continuing to pair cutting‑edge telemetry with community involvement, researchers hope to uncover the subtle factors that influence kestrel survival during the most vulnerable part of their annual cycle. The ultimate goal is a landscape where these vibrant falcons can thrive throughout the year, benefitting both biodiversity and the people who

Source: avian-behavior.org