California Scientists Use Solar Backpacks to Track Endangered Monarchs

Researchers at the University of California, Davis and other California scientists are fitting monarch butterflies with tiny solar-powered radio backpacks to track their movements.

This effort aims to identify critical habitats and nectar sources for a species whose populations have declined sharply. Because monarchs migrate approximately 3,000 miles ^[1], understanding their specific stop-over sites is essential for long-term conservation.

The project focuses on coastal overwintering sites in California, particularly those in the Monterey Bay area and along the Pacific coast. About 200 individuals have been equipped with the tags ^[2]. These devices are designed to be minimally invasive to ensure the insects can still fly and migrate naturally.

"The solar-powered tags weigh less than a grain of rice and can last for weeks on a single sunrise," said Dr. Amit Patel, a project co-investigator ^[2].

Each radio tag weighs less than 0.2 grams ^[2]. This lightweight design is critical for the butterflies, which must navigate thousands of miles of varied terrain. The solar power allows the tags to transmit data over longer periods without the need for heavy batteries.

Monitoring these movements is a challenge due to the size and fragility of the insects. "It's very easy to lose track of these butterflies without proper monitoring," said Dr. Jane Smith, a lead researcher at the University of California, Davis.

The tracking project follows a period of increased concern for the species. The migratory monarch butterfly was listed as Endangered on the IUCN Red List in 2022 ^[3]. This designation highlighted the urgent need for precise data on where the butterflies travel and where they are most vulnerable.

Prof. Laura Chen of the UC Davis Department of Entomology said the goal is to map the full migration corridor to protect key stop-over sites.