Tiny trackers reveal new details of monarch butterfly migration

Each year, swarms of monarch butterflies, known for their striking orange and black wings, embark on a 3,000-mile (4,800 kilometer) migration from southern Canada to overwintering forests of oyamel fir trees in central Mexico, a designated World Heritage site. Researchers have struggled to map these routes and understand the butterflies’ daily movements.

Approximately 1,750 monarchs have been fitted with solar-powered radio tags this year, providing unprecedented insights. The research aims to help rebound monarch populations, which face threats from habitat loss, pesticides, and climate change. “Pollinators are crucial to protect and ensure that our ecosystems remain healthy,” Quiñonez-Piñón stated.

The public can follow the progress of tagged butterflies via the free app, Project Monarch Science.

Many eastern monarchs pass through a narrow corridor in Texas, known as the “Texas funnel,” during their fall and spring migrations. Scientists are using the trackers to identify specific areas within Texas where the butterflies find water, nectar, and shelter.

Recent tracking data has revealed a surprising discovery: a monarch butterfly from Utah, west of the Rocky Mountains, has been observed joining eastern monarchs in central Mexico. Additionally, butterflies have been tracked migrating down the Eastern Seaboard to Florida, crossing the Gulf of Mexico, and traveling across Mexico – connections previously unconfirmed.

“We’re a year into it, and I think we’re all just thrilled,” said Emma Pelton, a senior conservation biologist with the Xerces Society. The new tags, developed by Cellular Tracking Technologies, weigh about as much as a drop of water and have overcome previous limitations of larger, heavier tracking devices.

Approximately 175 tagged butterflies have already been detected in Mexico since the tracking began.

To ensure the butterflies aren’t burdened, tags are applied to monarchs weighing over 400 milligrams. The process involves carefully catching and calming the insects before attaching the lightweight transmitters.

While the technology offers valuable insights, it’s important to note that it doesn’t provide precise location data, only detection points. Further studies are needed to assess any potential impact on butterfly behavior.

Monarch populations have declined significantly, with eastern monarchs decreasing by over 80% since the mid-1990s and western monarchs by about 95%. Threats include pesticide use impacting milkweed, the exclusive food source for monarch caterpillars, and climate change disrupting migration cues and causing extreme weather events. Conservation efforts are underway, including a lawsuit against the government regarding federal protections for monarchs, with a decision expected by 2030.