CAPE MAY — This year was good, but not great, for monarch butterflies migrating through Cape May.
The average number of the insects counted per hour by census takers at Cape May’s Monarch Monitoring Project was 47.1, compared to 94.09 last year, said Lindsey Cathcart, one of two monarch field naturalists there. But it was well above 2016’s average of just 14.71, she said.
It’s not necessarily that there were fewer monarchs this year, said Mark Garland, director of the project.
Scientists think prevailing winds through the heart of the migration pushed a lot of them further west, so they didn’t migrate through Cape May, he said.
The monarch census is a project of New Jersey Audubon’s Cape May Bird Observatory, and it sends counters out to slowly drive a five-mile route through parts of Lower Township and Cape May Point — counting every monarch butterfly they see in an hour.
The 20 mph drive and count is repeated every day at 9 a.m., noon and 3 p.m. from early September to early November and provides data for a census of monarchs passing through Cape May on their fall migration to Mexico.
Their migration takes them thousands of miles through the southeastern states to the Gulf of Mexico, then to the mountains about 62 miles north of Mexico City.
The numbers were well within the cycles of high years followed by low years that the project has seen in its more than 30 years of tracking monarch numbers, Cathcart said.
“It’s not outside of what we were expecting,” she said.
Some weeks were much better than others.
“Early October we saw a lot,” said Cathcart, who is from southeastern Pennsylvania near Pottstown. “Our best week was Sept. 29 to Oct. 5.”
That week averaged 137.4 monarchs per hour, she said. The highest day was Oct. 3, when census takers counted 271 monarchs in an hour.
There were no big spectacular roosts this year.
The temperatures were warm in October, so when winds were pushing them south they kept going right over the Delaware Bay.
“(The temperatures) were nice and warm, so they didn’t need to huddle up (in big groups),” Cathcart said. “They kept migrating through.”
She figured she and fellow monarch field naturalist Sarah Crosby, of Ridgewood, Bergen County, each tagged about 800 monarchs this year.
The process does not hurt the butterflies, which are captured in nets and handled gently as volunteers attach labels showing where they were tagged and when.
They are then promptly released.
The tagging has helped researchers better understand the monarch’s migration route and winter roost habits.
The project in total using volunteers tagged between 4,000 and 4,100, she said.
“Yesterday was a warm day, so we were out tagging still,” Cathcart said.
Last year, the monarch migration ran late, and the biggest day for census counters was Oct. 31, so the project decided to take counts for an extra week — extending it through the first week of November.
Even though this year’s migration wasn’t as late, the project will keep counting through Nov. 7, Cathcart said, so it can track changes in late migration over time.