Long distance wildlife tracking reveals waypoints from Jasper Ridge to Mexico

A Swainson's thrush with a radio tag on its back. Photo by Trevor Hebert.

This spring, Jasper Ridge joined the Motus network, an international collaborative research group that leverages radio signaling to track and monitor migratory animals. The Motus tower at Jasper Ridge has been successful in detecting band-tailed pigeons, and Motus tags installed on Swainson’s thrushes at Jasper Ridge have been detected as far south as Mexico.

The Motus Wildlife Tracking System was created by Birds Canada and is now an international collaborative research network with hundreds of locations using automated radio telemetry to track wildlife, especially small flying organisms such as birds, bats, and insects. Since May, Jasper Ridge has been a part of the Motus network with a new station installed and operated by the preserve’s technology specialist, Trevor Hebert.

From late June through mid-August, eight Swainson’s thrushes (Catharus ustulatus) were captured by mist nets at the Jasper Ridge bird banding station and fitted with Motus radio transmitter tags by certified bird bander Julian Tattoni. Each Motus radio tag broadcasts a unique ID associated with the individual, essentially functioning as a wireless bird band.

Migrating birds with radio tags are tracked as they pass near and are detected by Motus stations along their route. Detections from each station are then uploaded to the Motus database where they are combined with data from other stations to create a timeline and maps of a tagged bird’s movements.

The Motus tower station at Jasper Ridge Biological Preserve. Photo by Trevor Hebert.

The bird’s migration route is inferred by the line formed by sequential detections at Motus receivers. In most cases this route is not as precisely defined as it would be with a GPS device attached to the bird, but because of power, weight, and cost requirements of GPS, Motus can be a much better option for long-term studies, especially on small birds. Motus tags can be attached to other wildlife as well, including mammals and reptiles and even butterflies.

In September, the team was thrilled to learn that our first radio tagged Swainson’s thrush was detected at Ensenada and then soon after at San Quintin Reserva Natural Punta Mazo, both in Baja California, Mexico. Subsequently, four more of the eight tagged birds have been detected along their southward migration route, including two that have recently made it as far as the state of Sinaloa in mainland Mexico. The tracking data can be accessed here.

A map of  the US and Mexico showing Motus towers (points) and the migration of birds detected at Jasper Ridge Biological Preserve (connecting lines) including Swainson's thrushes which were tagged at Jasper Ridge and subsequently migrated south (orange lines).

Most intriguing is that four of the five birds made an open water crossing from California to Mexico, passing by Santa Catalina and San Clemente islands off the southern California coast. Birds stopped to rest in the area for up to 11 hours before moving further south. This suggests that these islands may be a critical waypoint for the Swainson’s migration.

These data will support continued conservation efforts along the Swainson’s thrushes’ migration. We don’t know yet where the final overwintering location for the Jasper Ridge Swainson’s thrushes is. Other studies suggest it may be southwestern Mexico where some have already arrived.

The Motus tower at Jasper Ridge has also been successful in detecting birds that were tagged elsewhere, including band-tailed pigeons. The California Department of Fish and Wildlife (CDFW) is monitoring band-tailed pigeons – the state’s only native pigeon - in response to long term population declines due to several factors including habitat loss and disease. Motus tagging will help CDFW understand the migratory patterns of the pigeons and the locations of critical habits that support them.

Motus technology will allow Jasper Ridge researchers to better understand the life history and migration of Swainson’s thrushes as well as the movements of other organisms as they move regionally and internationally. This can be especially useful for identifying and protecting critical habitats that birds and other migratory organisms depend on along their migration routes, as well as showing the connections between Jasper Ridge and other locations and how these amazing creatures connect ecosystems across great distances.

Learn more about the bird monitoring projects on our website: https://jrbp.stanford.edu/research/bird-monitoring

By Trevor Hebert and Adriana Hernandez, PhD

 Trevor Hebert is the academic technology specialist at Jasper Ridge Biological Preserve. He supports all research, education, and stewardship initiatives at the preserve through technological assistance.

 Adriana is the Assoc. Director of Research at Jasper Ridge Biological Preserve. Adriana's passion for biodiversity studies, collections-based research, and natural history has driven her to a research career in plant and evolutionary biology and conservation. Read about her background here.