Monarch butterflies at Natural Bridges State Beach
(Kevin Painchaud / Lookout Santa Cruz)
City Life

Cautious optimism blooms at Natural Bridges as monarch populations rebound from a dismal 2020

As the annual Thanksgiving count of the icon butterflies gets underway, the numbers are way up. But observers say it’s unclear what’s behind the big jump.

Back in the day, just a couple of decades ago, the monarchs at Natural Bridges State Beach could be experienced as immense fluttering clouds, or enormous vibrating masses hanging heavy from the eucalyptus trees.

Today, the populations of Western monarch butterflies at Natural Bridges and other “overwintering” spots along the California coast are, by comparison to what they once were, positively skeletal, like comparing the crowds at Main Beach on a sunny Fourth of July with those on a gloomy Thanksgiving Day.

So why are those who monitor the monarchs pleased, even elated, at what they’re seeing this month at Natural Bridges? They’re not thinking about the 1980s and ’90s, when monarch populations were at their peak. They’re thinking about 2020.

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Indeed, 20 to 30 years ago, monarchs overwintering in California could be counted in the millions. Last winter, according to the count of conservation nonprofit the Xerces Society, the number of monarchs spotted was less than 2,000 — that’s in the entire state, about a quarter of them (550) at Natural Bridges. That makes for a decline of approximately (gulp!) 99%.

This year, however, as the annual Western Monarch Thanksgiving Count gets underway in sites all over California, it appears the monarchs are bouncing back, however modestly. Early estimates of the still-arriving populations of butterflies are coming in at around 50,000.

Monarch butterflies at Natural Bridges State Beach
Monarch butterflies at Natural Bridges State Beach earlier this week.
(Kevin Painchaud / Lookout Santa Cruz)

Emma Pelton, a conservation biologist at Xerces, calls those numbers “fantastic,” but they should be kept in perspective.

“Even just four years ago, we had almost 200,000,” she said. “So it’s all relative. This is a much better year than the last three years. The numbers are way down when you kind of zoom out on their populations. But relatively this is a good year so far, because last year was so bad. (In 2020), people started to think, ‘Oh my goodness, maybe we’re too late, maybe the numbers aren’t ever going to come back,’ and this year gives us some hope that they are able to bounce up. And now we need to double down on our conservation efforts to get them to bounce even higher.”

For generations, the Monarch Trail at Natural Bridges State Beach on Santa Cruz’s Westside has entranced all kinds of visitors, from road-tripping tourists to field-tripping schoolchildren. Earlier this week, visitors flowed through the park’s boardwalk to gaze at the monarchs in the grove of eucalyptus and English ivy within the butterfly preserve. Individual butterflies crisscrossed the sky between branches. Docent Mary Guerrero was on hand to answer questions, and had set up a monitor for visitors to see the clusters of monarchs as they hung from the eucalyptus leaves. She explained that the monarchs prefer the narrow leaves of the eucalyptus over those of other trees because they are less likely to sway violently in the wind.

“There’s a great horned owl that hangs out here as well,” she said, pointing out that the owl keeps away the Steller’s jays that prey on monarchs.

Monarch butterflies at Natural Bridges State Beach
Counting clustered monarchs can be a challenge.
(Kevin Painchaud / Lookout Santa Cruz)

The Western Monarch Thanksgiving Count takes place each November to officially quantify monarch populations. Counts across the state have been ongoing since Nov. 13, but Saturday, teams of volunteers will gather to begin the official count of monarchs at Natural Bridges as well as other nearby sites, Lighthouse Field State Beach and Moran Lake.

Diana Magor is one of those volunteers. She said that the training program to count monarchs, developed by the Xerces Society, teaches volunteers, usually dispatched in pairs, to identify small clusters of monarchs — often difficult because the underside of their striking orange-and-black wings are brown and resemble dead leaves — and to estimate the size and number of such clusters in a given range.

“At the end of the count,” she said, “the two people in one counting party, they have to agree within 20% of each other on the number counted. If it’s 20% or less, they average their two numbers. If it’s off by more than 20%, you have to start all over again.”

Counting teams usually work early in the morning, or before the temperature passes 55 degrees, the point at which butterflies tend to leave their stationary clusters. “When they’re flying around, it’s harder to count them,” said Magor. There is another count in January, before the monarchs leave, to assess how many were lost to winter conditions.

A monarch butterfly at Natural Bridges State Beach
“The reality is that we don’t have a really good understanding of which pieces are the most important in the year-to-year fluctuations,” one biologist says of the monarch population.
(Kevin Painchaud / Lookout Santa Cruz)

Exactly why monarch populations are much more robust this year than last year is a source of speculation. Biologist Pelton warned against overly simplistic explanations, citing a wide variety of factors that could influence monarch numbers, from particular weather events to pesticide use to the availability of milkweed, without which monarchs cannot survive. Fluctuations in monarch populations, in fact, serve as a compelling illustration of the complexity and interdependence of nature.

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“That’s the great takeaway here,” said Pelton. “We’re seeing a lot of folks getting really excited and it’s human nature to want to see patterns and say, ‘It was this, or it was this.’ But the reality is that we don’t have a really good understanding of which pieces are the most important in the year-to-year fluctuations. And that’s OK. These are insects.

“They move over huge areas in multiple generations. So it’s really hard to pinpoint (specific factors). But they probably had some good conditions this year. They had a warm, dry summer, which they tend to like. And they probably had some good luck early in the season. So that’s amazing. And now we can think about some of the other pieces that play a role in the things that matter a lot more than why this year might be slightly better than last year.”

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