CHANNAHON, Ill. (CBS) — Volunteers in Will County track monarch butterflies in a beautiful combination of low-tech physical work and a high-tech database.

The great monarch migration is under way, as the butterflies head south to Mexico.

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Volunteers track the monarchs with the well-placed sweep of a butterfly net. It brings in more monarchs than CBS 2’s Ed Curran had ever before seen in one place at one time.

Lori and Roger Gill of Channahon will let smaller monarchs go, because they probably won’t survive the flight to Mexico. But before the bigger ones leave, they get a number.

The butterflies are tagged with tiny stickers. They are cataloged in male and female groupings, and the numbering system becomes part of a database.

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We’re nearing the end of the butterfly migration for this Fall. In Illinois, there are a number of places they stop to rest – and their journey often takes them right down Route 66.

It was along Route 66 where we saw this amazing mass of monarchs.

One Orland Park woman who raises butterflies and puts stickers on them recently had one of her butterflies spotted in Mexico.

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Learn more about the butterfly migration at the Butterfly Monitoring Network.