They are renowned for their fantastically long migration routes, with most populations east of the Continental Divide taking several generations to head north from their wintering areas in Mexico to the United States and Canada, returning each fall in a spectacular continuous mass migration flight numbering in the millions to a single spot in the mountains of central Mexico.
Migrating monarch butterflies have long been observed in New Mexico in September and October, including at the Bosque del Apache National Wildlife Refuge south of San Antonio.
In 2016, right after wintering birds flew north, monarch butterflies were sighted for the first time during their spring migration at the refuge. Not much is known about the habits of monarchs in New Mexico, so their appearance in April caused a stir.
Refuge biologists began surveying sites where the insects were frequenting, and found that some monarchs are spending the entire summer on the refuge, laying eggs on native horsetail milkweeds (also known as Western Whorled milkweed) growing on the ditch banks and in the farm fields.
This spring, Bosque del Apache staff biologist Megan Goyette started the Monarchs Along the Rio Grand citizen science project so anyone can be a part of the refuge’s monarch study.
It’s simple: just take a photograph of a monarch butterfly or caterpillar and upload the information onto the project’s website www.inaturalist.org/projects/monarchs-along-the-rio-grande-in-new-mexico. A biologist will review the photographs to confirm the sighting and then upload the information to the website for other observers and scientists to view.
Monarchs are colorful, which makes them easy to spot, whether they are in their butterfly or caterpillar stage. The butterflies sport bright orange-paned wings with black edges enclosing white dots, often folded in a V as they float on the wind. Because their proboscis (a tubular tongue) is fairly long, monarchs can sip nectar from a variety of flowers, according to Steve Cary, author of “Butterfly Landscapes of New Mexico.”
Monarch butterflies have been seen visiting alfalfa flowers and sunflowers down in the valley and chamisa (rubber rabbitbush) in the uplands, Goyette said. A cellphone photo of a monarch on a flower will provide important data for biologists planning restoration projects protecting plants the butterflies prefer.
Monarch caterpillars eat poisonous milkweeds, an adaptation that gives them and the adult butterflies a bitter taste that repels predators. Two other butterfly species common in New Mexico have taken advantage of their cousins’ adaptation by mimicking the monarch’s coloration.
The viceroy butterfly looks very similar, but it is smaller and has an additional thin black band crossing its hind wing. Darker, brownish-orange wings spotted all over with white dots and a less prominent black edge mark the desert queen butterfly.
Observers can download apps for their smartphone to help identify monarchs. Goyette likes Journey North and Monarch SOS, which are compatible for both Androids and iphones.
Monarchs breed in New Mexico in late spring, Cary said. In May and early June, most of the monarchs in New Mexico are in the caterpillar stage. The caterpillars are bright yellow with prominent black stripes and eat only milkweed plants.
Scientists don’t know exactly how the monarchs utilize the different milkweed species, so observations are critical. Although it’s harder to spot a creeping caterpillar than a flying orange butterfly, caterpillar observations are especially important for scientists seeking to understand monarch life cycles, Cary said.
Monarch butterflies can be observed in New Mexico from spring through early fall, but they are most numerous in September and October. Last September, the Bosque del Apache NWR conducted its first monarch tagging event. Goyette said tagging butterflies in the fall provides the same kind of information for scientists as banding wintering ducks – population numbers and migration patterns.
In 2016, volunteers, staff biologists and San Antonio School students caught 65 butterflies on the refuge and put a small numbered sticker on the outside of each butterfly’s wing. This fall, they hope to tag over 100 butterflies. Observers should take a photo or note the sticker number and location of a tagged butterfly on www.inaturalist.org or contact the refuge at 575-835-1828.
Monarchs in trouble
Monarch butterflies have been in serious decline for the past 20 years. According to the U.S. Fish and Wildlife Service, numbers have declined from 700 million in the 1990s to fewer than 140 million now.
USFWS scientists say this year alone, the number of monarchs overwintering in Mexico declined by 27 percent compared to last year, probably due to one storm event in their small Mexican wintering area that wiped out millions of the butterflies.
Scientists blame the decrease on an increased frequency of severe storms triggered by climate change in their overwintering areas and habitat reduction. Monarch larvae feed only on native milkweed species, which are being eradicated, especially in farm fields where the toxic plants are considered noxious weeds.