Narrow bridges

Cautious optimism blooms at Natural Bridges as monarch populations rebound after bleak 2020

Back then, just a few decades ago, the monarchs of Natural Bridges State Beach could be seen as huge floating clouds or huge vibrating masses hanging heavily from eucalyptus trees.

Today, the western monarch butterfly populations of Natural Bridges and other ‘wintering’ sites along the California coast are, compared to what they once were, positively skeletal, as compare Crowds of Main Beach on a sunny July 4th with those on a gloomy Thanksgiving Day.

So why are those who watch the monarchs happy, if not thrilled, with what they’re seeing this month at Natural Bridges? They don’t think of the ’80s and’ 90s when monarch populations were at their peak. They think about 2020.

Indeed, 20 to 30 years ago, the monarchs wintering in California numbered in the millions. Last winter, according to the nonprofit conservation tally on Xerces Company, the number of monarchs spotted was less than 2,000, that is, statewide, of which about a quarter (550) were at Natural Bridges. That’s about a (gulp!) 99% drop.

This year, however, as the Western Monarch Thanksgiving Account starts at sites all over California, it seems like monarchs are bouncing back, even modestly. Early estimates of populations of butterflies that are still arriving are around 50,000.

Monarch Butterflies at Natural Bridges State Beach earlier this week.

(Kevin Painchaud / Santa Cruz Belvedere)

Emma Pelton, conservation biologist at Xerces, calls these numbers “fantastic,” but they need to be put into perspective.

“Even just four years ago, we had almost 200,000,” she said. “So everything is relative. It’s a much better year than the last three years. The numbers are very low when you zoom out on their populations. But relatively, it’s been a good year so far, because last year has been so bad. (In 2020) people started to think, “Oh my God, maybe we’re too late, maybe the numbers will never come back”, and this year gives us some hope that they are able to bounce back. And now we need to double our conservation efforts to bounce them even higher. “

For generations, the Monarch Trail at Natural Bridges State Beach in the Westside of Santa Cruz has fascinated all kinds of visitors, from traveling tourists to schoolchildren. Earlier this week, visitors walked through the park promenade to gaze at monarchs in the eucalyptus and English ivy grove in the butterfly reserve. Individual butterflies crisscrossed the sky between the branches. Docent Mary Guerrero was on hand to answer questions and set up a monitor so visitors could see groups of monarchs hanging from eucalyptus leaves. She explained that monarchs prefer the narrow leaves of eucalyptus over those of other trees because they are less likely to sway violently in the wind.

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

Monarch Butterflies at Natural Bridges State Beach

Counting monarchs grouped together can be a challenge.

(Kevin Painchaud / Santa Cruz Belvedere)

The Western Monarch Thanksgiving Count is held annually in November to officially quantify monarch populations. Statewide counts have been ongoing since November 13, but on Saturday volunteer teams will meet to begin the official monarch count at Natural Bridges as well as other nearby sites, Lighthouse Field State Beach and Moran. Lake.

Diana Magor is one of these volunteers. She said the training program for counting monarchs, developed by the Xerces Society, teaches volunteers, usually sent in pairs, to identify small groups of monarchs – often difficult because the undersides of their striking orange and black wings are brown. and looks like a dead man. leaves – and estimate the size and number of these clusters in a given range.

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

Count crews typically work early in the morning or before the temperature rises above 55 degrees, the point at which butterflies tend to leave their stationary clusters. “When they fly, it’s harder to count them,” Magor said. There is another count in January, before the monarchs leave, to assess how many have been lost due to winter conditions.

A monarch butterfly at Natural Bridges State Beach

“The reality is, we don’t quite understand which parts are the most important in year-to-year fluctuations,” says a biologist of the monarch population.

(Kevin Painchaud / Santa Cruz Belvedere)

It is a matter of speculation exactly why monarch populations are much more robust this year than last year. Biologist Pelton cautioned against overly simplistic explanations, citing a wide variety of factors that could influence monarch numbers, from particular weather events to pesticide use to 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.

“It’s the big takeaway here,” Pelton said. “We see a lot of people getting really excited and it’s human nature to want to see role models and say, ‘It was this, or it was that. “But the reality is we don’t have a very good understanding of which parts are most important in year-to-year fluctuations. And that’s OK. They’re bugs.

“They move over large areas over several generations. It is therefore very difficult to pinpoint (specific factors). But they’ve probably had good conditions this year. They’ve had a hot, dry summer, which they tend to like. And they were probably lucky at the start of the season. So it’s amazing. And now we can think of some of the other pieces that play a part in things that matter a lot more than why this year might be slightly better than last year.

More from Wallace Baine