A new technology is providing a previously impossible window into monarch movement patterns, documenting amazing information and a surprising amount of variation. This technology involves placing tiny solar-powered transmitters (Blū+ tags) to monarchs’ thoraxes. These transmitters weigh about as much as a grain of rice, and send location signals that can be detected by Bluetooth-enabled phones up to about ¼ mile away. The phones are essentially passive receivers that allow detection of fine-scale movements. In 2025 about 400 transmitters were deployed; this number has almost quadrupled in 2026.

Photo by Jim Otto

The second half of August is a particularly interesting time to observe monarchs in their northern breeding range. Beginning on about August 15, monarchs emerge from their pupae in diapause. Responding to cues that include both daylength and sun angle, these adults do not become reproductive soon after emerging.
Photo by Tom Koerner/USFWS

The first monarch generation of 2026 began as eggs in the southern US, the offspring of monarchs that had overwintered in Mexico. These first-generation monarchs continued the journey northward, arriving in Wisconsin in late April and May, laying eggs as they moved north.
Photo by Laura Perlick / USFWS

Monarchs from the generation that emerged last autumn began heading north from Mexico in March, laying eggs along the way. By now, that generation has died, and their offspring are continuing the journey northward. Based on counts from CONANP and the World Wildlife Fund-Mexico, about 64% more monarchs headed northward in spring 2026 than in 2025.
Photo by TexasEagle

From early November until mid-March, most Eastern North American Migratory monarchs were in Central Mexico, waiting to head back north to produce what will become the first new generation of 2026. Estela Romero of Journey North reported early departures in late February, and final massive departures on March 7 and 8. These monarchs, most of whom began their lives as eggs in monarchs’ northern breeding grounds last August and September, are now heading north, laying eggs along the way.
Photo by Brenna Weisner