Officials say they counted fewer numbers of monarch butterflies during their annual migration through Cape May in New Jersey this year.
Monarch field naturalist Lindsey Cathcart tells The Press of Atlantic City that members of the city’s Monarch Monitoring Project counted an average 47.1 insects per hour this year, compared to 94.09 last year.
The migration season began on September 1 and generally ends around October 31. Cape May is a strategic stopover for the 3,000 mile migration from Canada to Mexico.
Project director Mark Garland says the numbers don’t necessarily mean there were fewer monarchs. He says scientists believe winds may have pushed the butterflies further west.
Cathcart says this year’s count is well above 2016’s average of 14.71 butterflies per hour. She says volunteers have tagged between 4,000 and 4,100 insects, and their best week was Sept. 29 to Oct. 5.
The project will continue to count butterflies through Wednesday.
Last season featured the highest monarch counts in four years, with warm weather resulting in a late season influx.
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 percent 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 is because a main factor hurting monarchs worldwide isn’t as big of an issue here: the killing of milkweed plants by herbicides in Midwestern farm country.
“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!”
The Associated Press contributed to this report.