By early September, the annual migration of monarch butterflies was impossible to miss.

During two hours of birding at Armour Hill, I counted at least 50 streaming past. Back home, another 20 or more were feeding in our yard, most of them on Ageratum, our undisputed monarch favourite. Only three or four had been in the yard over most of the summer, so these were almost certainly migrants passing through.

Over the next few days, I saw more wherever I went, all following a purposeful southwesterly course as part of the vast migration to the mountain forests of central Mexico where they overwinter.

It has been a banner year for monarchs in the Kawarthas, maybe the best I can remember. There are several contributing factors. The population occupying the Mexican wintering forests in 2025—26 had increased by 64 per cent, from 1.79 to 2.93 hectares — the largest area recorded in seven years, although still far below the enormous concentrations of the late 1990s.

Monarchs also appeared unusually early in the Kawarthas, with many reported in May. Generally favourable summer weather then helped milkweed and nectar plants flourish. Because females can lay several hundred eggs, numbers can increase dramatically through successive generations when weather and habitat co-operate. Still, one excellent summer does not mean that the monarch’s long-term decline has been reversed.

High-tech tracking for the journey south

Two of the monarchs that visited our yard are now helping to provide a new glimpse into their fall migration. On Sept. 16, Erin McGauley, a professor at Fleming College’s School of Environmental and Natural Resource Sciences, captured two females on our Ageratum. These late-summer monarchs belong to a remarkable “super generation.”

Unlike those born earlier in the summer, which generally live two to four weeks, migrants can survive for eight or nine months. They postpone reproduction and devote their energy to migration and surviving the winter. In spring, they begin the journey north, lay eggs and die; their descendants........

© Peterborough Examiner