Scientists are tracking monarch butterflies using solar-powered radio tags to map their migration routes and identify critical stopover sites. Rebeca Quiñonez-Piñón, senior scientist at the National Wildlife Federation, led the effort to attach nearly 1,750 tags to monarchs this year as part of a trinational tracking study.
The tags weigh about as much as a drop of water and cost $200 each. They were developed by Cellular Tracking Technologies. Monarchs are caught with nets, positioned on a special board with their legs and antennae protected, and then the adhesive tag is gently pressed to their abdomen before release. Quiñonez-Piñón said that if applied correctly, "the monarch will be completely safe."
Monarchs travel roughly 3,000 miles from southern Canada to central Mexico's oyakel fir forests each fall. Scientists have long struggled to document their exact routes and daily flight distances. Only some monarchs migrate. A large portion of eastern monarchs funnel through Texas twice yearly, heading south for winter and north again to breed.
Since tracking began last year, about 175 tagged butterflies have been detected in Mexico. The data revealed new migration patterns, including the first evidence of a western butterfly from Utah joining eastern monarchs in central Mexico, and butterflies traveling down the Eastern Seaboard to Florida before crossing the Gulf of Mexico. Emma Pelton, senior conservation biologist with the Xerces Society for Invertebrate Conservation, said "we're all just thrilled," noting that older tracking devices proved too heavy.
Louie Yang, an insect ecologist at the University of California, Davis, called the technology "pretty remarkable" but noted limitations. The system detects where receivers picked up signals rather than providing exact locations, and detection does not confirm a butterfly remains alive. Yang said further studies will be needed to understand how the tags affect butterfly behavior.
Eastern monarch populations have declined more than 80% since the mid-1990s, and western populations have dropped about 95%. Tierra Curry, senior scientist at the Center for Biological Diversity, cited pesticides that threaten milkweed, the plant where monarchs lay eggs. Climate change causes temperature shifts that disrupt migration cues and can kill butterflies caught in unexpected freezes. Prolonged drought dries up water and nectar sources. The public can follow individual butterflies on the free app Project Monarch Science.