Monarch Butterfly Migration Under Threat in North America

Monarch Butterfly, photographed in Tauranga, New Zealand. © John Corney

Note: I first wrote this post around 2010–2011, after a summer in which I'd barely seen a single monarch in Southern California. I've updated it in 2026 with the current status of the monarch population, which has shifted in important ways since then — some of it, encouragingly, for the better. My original observations are kept below as a record of what things looked like then.

If you look through my photography, you'll notice how much of it is taken in the great outdoors — landscapes, flora, and fauna. I love to catch a shot of any bird or animal I encounter along the way.

One thing you won't see much of, though, is butterflies. That's simply because I don't encounter many as I move around Southern California and the Southwest.

The Monarchs That Weren't There

Back when I first wrote this post, monarch butterflies had been much on my mind — because of their absence. If you lived in Southern California then, you'll remember how few there were to be seen. I hadn't spotted a single one all summer, and recalled seeing very few in the summers before.

That spring I planted a couple of milkweed plants in my yard, and waited. No caterpillars showed up. Yet when I was home in New Zealand in early May that year — late autumn in the Southern Hemisphere — there were monarchs all over the parts of central Auckland where I was spending my time. A real delight to see, and a pointed contrast with home.

There are two butterfly gardens close to me here in Irvine: one at the San Joaquin Marsh and another at Mason Park. Both have been established for years, planted with milkweed and nectar plants. Yet I had hardly ever seen a monarch at either — the odd swallowtail, and that was about it.

What's Happening to the Monarch

When I first looked into it, I found that monarchs were in serious decline across North America — and that broad picture, unfortunately, still holds. Scientists estimate that around 970 million monarchs have vanished since 1990. Since monitoring began in the 1980s and 1990s, the eastern population has declined by roughly 80%, and the western population — the one that overwinters along the California coast, and so the one most relevant to those of us in Southern California — has declined by more than 99%.

The causes are multiple and tangled together. Habitat loss is central: the loss of wild milkweed, which monarchs need to lay their eggs on, and of the nectar flowers the adults feed on. In the agricultural Midwest, the widespread adoption of herbicide-tolerant crops allowed far more thorough weed control across vast areas, and milkweed was among the casualties — a significant factor in the eastern population's decline. But it isn't the whole story. Climate change, drought along the migration routes, pesticide use, disease, and the degradation of the overwintering forests in Mexico and the overwintering groves in California all play their part. The western collapse, in particular, isn't explained by Midwest agriculture at all.

The Picture in 2026 — Some Hope, and a Warning

Here is where the story has genuinely changed since I first wrote this post, and it's worth being precise about the two different monarch populations, because they're doing very different things.

The eastern population — cautious good news. The monarchs that migrate between Canada and Mexico are counted each winter by measuring the area of forest their colonies occupy in central Mexico. In the survey released in March 2026, covering the winter of 2025–2026, the colonies occupied 2.93 hectares — a 64% increase over the previous winter's 1.79 hectares, and the second year of increase in a row. That figure is even slightly above the average for the past decade. It's real, welcome news. For perspective, though, the same forests held more than 18 hectares of monarchs back in the winter of 1996–1997, so "above the recent average" still means far below historic norms.

The western population — still in crisis. The monarchs that overwinter along the California coast are the ones I'd most hope to see here in Irvine, and their news is not good. The Xerces Society's annual Thanksgiving count, taken in late November 2025, recorded just 12,260 butterflies — the third-lowest total ever recorded. Researchers consider roughly 30,000 to be the threshold below which the population risks a kind of collapse from which recovery becomes very difficult. The western count has been hovering below that mark for years.

A possible Endangered Species Act listing. In December 2024, the US Fish and Wildlife Service proposed listing the monarch as a "threatened" species under the Endangered Species Act, together with the designation of several thousand acres of the western population's California overwintering sites as protected critical habitat. As of early 2026, that rule has not been finalised — the timeline has slipped, and a final decision isn't expected before late 2026 at the earliest. If it goes through, it would be the most significant legal protection the monarch has ever received.

What We Can Do

The encouraging thing about monarchs is that ordinary gardeners genuinely can help — monarch recovery depends on exactly the kind of small, distributed habitat that backyards, schools, parks, and roadsides can provide.

The single most useful thing is to plant native milkweed — and the emphasis on native matters. Milkweed is the only plant monarch caterpillars can eat. Just as important is planting a succession of nectar flowers to feed the adults through the seasons. The Monarch Watch website, which I first discovered when researching this post all those years ago, is still going strong and has excellent guidance on establishing monarch "Waystations" in your own backyard or community.

One word of caution I'd add now that I didn't know to give back then: here in California, plant narrow-leaf milkweed (Asclepias fascicularis) or another California-native species, rather than the widely sold tropical milkweed (Asclepias curassavica). Tropical milkweed doesn't die back in winter in our mild climate, and that can disrupt the monarchs' natural migration cycle and spread a harmful parasite. It's worth asking specifically for native milkweed at the nursery.

When I first wrote this post, I'd just planted 48 seeds from my own milkweed plant, hoping some SoCal friends would take the seedlings for their own gardens. The hope behind that small act still stands — and in 2026, with the eastern population showing what recovery can look like when conditions allow, it feels a little less like shouting into the wind.

Let's do our part to increase the habitat available to the monarch. I'd genuinely like to hear how things are where you live — do you see monarchs in your area? Are there more, or fewer, than there used to be? Post a comment below.