Monarch butterfly researchers report biggest numbers of season this week in Cape May

A monarch butterfly in Cape May, New Jersey. (Courtesy of Mark Garland)

A monarch butterfly in Cape May, New Jersey. (Courtesy of Mark Garland)

Like clockwork, the monarch butterfly migration season along the Jersey Shore is heating up.

Driven by winds and temperatures, the migration season, when the butterflies head to Mexico for the winter, begins on Sept. 1 and generally ends around the end of October, or until the first freeze.

In Cape May — which is a strategic stopover for a 3,000-mile migration from Canada to the Transverse Neovolcanic Mountains in Mexico — the Monarch Monitoring Project announced that the “biggest numbers” of the season were recorded on Monday after a steady increase in the last week.

According to the organization, in its 30th year of netting, counting, and tagging, monarchs are generally found in Cape May Point dune crossovers. The organization advises not to leave the formal pathways on the beach because it can harm the butterflies.

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Volunteers net the butterflies, measure and assess their winds, and affix a coded tag for tracking purposes. In 2017, the organization reported the highest monarch counts in four years, with warm weather resulting in a late-season influx. But in 2018, the numbers decreased significantly.

In 2014, Sarina Jepsen of the Xerces Society, one of the three conservation groups petitioning the federal government for protected status, told WHYY that the monarch populations counted at wintering sites in Mexico have declined by about 90% in 20 years.

The causes, she says, are a loss of habitat and the decrease in available milkweed, the monarch caterpillar’s only food.

At the time, Cape May Bird Association’s Chris Tonkinson hypothesized that it’s because herbicides that kill milkweed in places like the Midwest aren’t necessarily found on the East Coast.

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“The monarchs that have made their way to the upper Northeast, as they come down the East coast they’re not as exposed to that big agriculture phenomenon,” Tonkinson said, “So there’s a lot more habitat and milkweed for them comparatively.”

The Monarch Monitoring Project encourages people to plant milkweed.

“Planting a milkweed patch creates an entire community of organisms that both depend on the milkweed and each other for survival,” an organization blog post states. “If you have a patch of milkweed at home, keep a lookout for these other milkweed dependent bugs, and you can start to look at the milkweed patch not only as food for monarchs, but as a village with many different residents!”

Federal officials are investigating whether to place monarchs on the endangered species list.

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