CAPE MAY POINT, N.J. (AP) - The number of monarch butterflies migrating through the Point fell by more than half this year, according to an annual hourly census study, but it may be more because of the weather than a population change.
“We had strong easterly winds for much of September,” Monarch Monitoring Project Director Mark Garland told The Press of Atlantic City (https://bit.ly/2ei7Job) this week.
That may have pushed butterflies farther west, rather than staying at the coast, he said.
New Jersey Audubon’s Cape May Bird Observatory has been running the project for 25 years, counting monarchs three times daily in five-mile routes around the Point from Sept. 14 through Oct. 31.
Garland said this year was the third-lowest hourly count the volunteers have made in all that time.
The hourly average of monarchs counted by the project this year on the census route was 15, compared with an hourly average of 38 last year, according to data provided by Garland.
The high was about 360 an hour in 1999 and the low was 8.9 per hour in 2004 after a bad winter killed off many butterflies.
“This year never got real good, but it was never real bad either,” said Garland, adding that numbers were low but steady all season.
Most years there is more variation week to week, he said.
“We have to wait and see what the numbers are in Mexico,” he said of counts in their wintering grounds, to know if this year’s count signifies a population drop or simply a change in migration route.
In addition to counting the insects, volunteers and staff members also tag them to better understand their migration, and offer regular educational workshops to the public.
The tagging is continuing, Garland said, since there are more late migrators this year than most years.
“Late in the season we are seeing more monarchs than usual,” he said of late October into November. “The early reports from Mexico say a lot have already arrived at the winter grounds. But we are still tagging. Is this the result of climate change pushing the migration later?”
Past tagging has shown that those that pass through earlier in the season have a better chance of surviving in Mexico, Garland said.
“Time will tell,” said Garland. “One year means nothing, but a trend for multiple years would be different.”
Most monarchs traveling from the East Coast spend the winter huddled together in trees on land now protected as the 200-square-mile Reserva de la Biosfera Mariposa Monarca (Monarch Butterfly Biosphere Reserve), about 62 miles northwest of Mexico City.
Monarch butterflies have the longest migration of any butterfly species, and they are loved by many people simply for their beauty.
Thousands of people visit Cape May each autumn to see the colorful orange and black insects come through in large numbers, contributing to ecotourism here.
But as pollinators they also have a role in helping flowering plants thrive and produce fruits, vegetables, tree nuts and ornamental flowers, according to MonarchWatch.org.
“Every third bite of food we eat comes to our table courtesy of a pollinator. Monarchs, bees and many other pollinators share much of the same habitat - so what happens to monarchs, happens to other pollinators,” according to Monarch Watch Conservation Specialist Candy Sarikonda.
The program at Cape May has discovered through its tagging program that monarchs that migrate through here stay east of the Appalachian Mountains until they get to the Gulf Coast, then follow the gulf to Texas, and then to Mexico.
While monarchs nationally have experienced a 90 percent decline in the past 20 years, the data collected here has shown a more stable population overall, with ups and downs from year to year.
Garland thinks that means there is a better milkweed supply for the Northeast population than for populations that mainly migrate over the Central Plains.
Monarch butterflies only lay their eggs on plants in the milkweed family, because the larvae eat only those plants.
But the insects also face disease, parasitic wasps that lay their eggs in monarch caterpillars, death from severe weather and a shrinking overwintering forest in Mexico, MMP Field Coordinator Louise Zemaitis has said. She has worked on the project for decades.
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Information from: The Press of Atlantic City (N.J.), https://www.pressofatlanticcity.com
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