Tagging monarchs at Grand Canyon and Dinosaur: a summer of intern fieldwork

A butterfly tagged at Stewart Lake State Wildlife Area along Utah's Green River was recaptured 111 miles south along the Colorado River near Moab, and a biologist says the Green River is likely a travel corridor for monarchs. Interns Cassandra Cavezza and Juan Pablo Esparza-Limón describe their summer of monarch work in an article published in the Winter 2022 issue of the National Park Service's Park Science magazine. They worked through the Latino Heritage Internship Program, which works with the Park Service and Environment for the Americas, at Grand Canyon National Park and Dinosaur National Monument.

A butterfly in decline

The article says monarch numbers in North America have collapsed by more than 80 percent since 2005, and western populations are down 99 percent since the 1980s. The causes include pesticides, loss of food plants, disease, habitat loss and climate change, which also disrupts milkweed, the only plant monarch caterpillars eat. A parasite can deform wings and hinder flight. In 2020 the U.S. Fish and Wildlife Service decided that listing the monarch under the Endangered Species Act was warranted but precluded by higher priorities, and a 2022 review kept that finding, with a listing priority number of 8 on a scale of 1 to 12 (lower means higher priority). The agency planned to reevaluate in 2024.

Eastern monarchs fly to Mexico and western monarchs to the West Coast; arrows show flight paths. NPS illustration by Sarah Sparhawk.

The two populations are separated by the Rocky Mountains. Western monarchs winter mostly on the central California coast, with others in southwestern deserts and some in Mexico. In spring they fly inland and north in a relay of four generations across about 3,000 miles. The first three generations live about four weeks as breeders. The fourth, the "mega-migrators," pause reproduction to survive winter and live up to nine months. Eastern monarchs winter in the oyamel fir forests of the central Mexico highlands. The article adds that some Mexican cultures see monarchs as the souls of departed relatives, returning for a night at Día de los Muertos in early November.

Monarchs at Amistad National Recreation Area, Texas, on their fall migration to central Mexico. NPS photo.

What the interns did

Grand Canyon and Dinosaur, 500 miles apart, share a feature: both lie on tributaries of the Colorado River Basin, and their river edges have the milkweed and nectar plants monarchs use. Throughout the summer the interns:

• Grew habitat. At Grand Canyon, Cavezza helped inventory seeds, grow seedlings in the South Rim greenhouse and plant them at the park's two monarch habitat sites, one on each rim. She also made a short video called "Milkweed and Monarchs."
• Tagged butterflies. Both parks work with the Southwest Monarch Study to confirm migration routes. Interns and staff caught wild adults, stuck lightweight waterproof ID stickers on a wing and released them. Each tag carries a number and a contact address for anyone who finds the butterfly. Lynch, a biological technician with Ashley National Forest, credited the success to unusual collaboration among agencies, and a survey effort covers twelve locations with milkweed.
• Checked for the parasite. At Dinosaur, Esparza-Limón helped run Project Monarch Health, a citizen science project with the University of Georgia. Clear stickers pressed on captured monarchs' abdomens collect parasite samples. The parks shared tagging and parasite data with scientists and the Utah Pollinator Pursuit survey.
• Taught. Cavezza taught third graders at the Grand Canyon School about the life cycle and tagging, using a puppet to show how to capture a monarch safely. Esparza-Limón helped design evening ranger programs on monarch life stages and invited 50 eighth graders to an interactive program with insect nets.

The tag is a lightweight adhesive sticker bearing the butterfly's ID number and an email address for reporting a sighting. NPS photo by Juan Pablo Esparza-Limón.

The Southwest Monarch Study coordinator, Gail Morris, said that after tagging more than 22,000 monarchs and recovering 75, researchers know that those with excellent wing condition, or newly emerged, are the likeliest to reach a wintering site. The Moab recapture suggests the Green River is a travel corridor.

Highlights and lessons

The interns swapped parks for training, co-hosting a public tagging event at Dinosaur and planting milkweed at Grand Canyon's Pima Point pollinator garden with a Zuni Pueblo crew from the Ancestral Lands Conservation Corps. Both took first-time river trips: Cavezza rafted nine days through the Grand Canyon on a crew working against invasive plants and protecting cultural sites, and Esparza-Limón joined a four-raft, multi-day survey of the Green River in mid-September, near the peak of migration. On the second day the group caught a newly emerged monarch and tagged it just before its first flight.

A monarch chrysalis blends into the plants; spotting one in the field is rare. NPS photo by Juan Pablo Esparza-Limón.

Cavezza came away sure of a career in environmental science. Esparza-Limón, a geologist, now hopes for a Park Service career and wants to widen access to the agency for Latinos and other underrepresented groups. They end on optimism, quoting an Ashley National Forest biologist's line that one person may move a few boulders but many collaborators can move mountains.

Sources

• National Park Service, Park Science magazine, For the Love of Monarchs: How We Joined the Push to Save a Beloved Butterfly, by Cassandra Cavezza and Juan Pablo Esparza-Limón; rewritten in hubnx's own words. Interns' and partners' words are paraphrased; photographs of people, including students, are not reproduced.