How do you keep tabs on a butterfly?

Monarch butterflies perform one of the  most amazing feats in the natural world:   some crossing a continent, traveling  3,000 miles from Canada to Mexico in   a multi-generational migration and settling  in the same special places year after year   after year… even though these individual  butterflies have never been there before.

Unlike most butterflies, monarchs fly high—riding  thermals over 3,000 feet above the ground.

And   during migration, they can speed along at  5-8 miles an hour, maybe a little faster   than most of us jog.

So, it can be really hard to  follow a single butterfly over their long trip.

And it wasn’t until the 1970s that  American and Canadian scientists   began to understand the full scope of  this journey.

To them, it was a mystery   where monarchs went during the winter.

But  for thousands of years, people in Mexico,   and likely in coastal California had known where  the monarchs were spending the colder months.

Now, there’s a new kind of monarch disappearance  mystery: Why are their numbers plummeting?

In the Western U.S., monarch numbers  have dropped from as many as an   estimated 10 million butterflies in  the 1980s to less than 2,000 in 2020.

To find out what’s happening, researchers  are harnessing the power of new technology   and community scientists to  track monarchs in California.

So butterflies are in the order Lepidoptera.

We thought for a long time butterflies and   moths had a clear distinction.

But then a lot  of genetic information seemed to suggest that   instead maybe there isn’t really like a clear  scientific distinction between the two groups.

We thought that maybe butterflies flew in the  day, but it turns out there's day flying moths.

Lepidoptera tend to have scales on  their wings.

They’re all holometabolous,   which means they have complete metamorphosis.

There are other insects that have incomplete  metamorphosis, like grasshoppers.

Like,   a baby grasshopper kind of just looks  like what an adult grasshopper looks like.

But for holometabolous insects, they have  an egg that hatches to a caterpillar.

The   caterpillar goes through a series of instars,  a series of molts to a larger and larger size.

Then they go into a pupal stage which is  what these are, and in the pupal stage,   there is a complete kind of internal and  external rearrangement of their body,   and then they emerge as an adult.

Because they’re turning into  monarch soup inside that pupal case,   it makes it particularly difficult to track an  individual between life stages.

You might be able   to catch a slower moving caterpillar, but a tag  wouldn’t transfer over to a winged adult’s body.

For monarchs there's multiple generations   that go varying distances along the  journey from Canada down to Mexico.

The round-trip takes 3-5 generations  to complete.

Most of those will only   live about 2-6 weeks, mating and  laying eggs during the summer   months.

But one “super” generation  is born in late summer, early fall.

DIRECTOR: Ah, so it’s that super generation  that does the longest leg of migration?

JESSICA: Yeah, and if you get a chance to see  them gathered at an overwintering site, it’s truly   stunning.

From October through March, monarchs  aggregate in particular spots.

Eastern monarchs   make their way to Mexico, and most western  monarchs wing their way to spots on the California   coast.

We already know where many of these sites  are based on decades of observational data.

ASHLEY: I think it’s really special that  they overwinter basically really in your   face on the coast of California, with  thousands of them hanging out together.

JESSICA: Conservation biologists Ashley Fisher  and Isis Howard are researchers with the Xerces   Society, a science-based nonprofit focused  on conserving invertebrate species.

They’re   tracking monarchs during their stay in California  to understand changes in populations over time,   and what factors might be causing  the big declines in their numbers.

ISIS: What we see here are monarch butterflies  that have traveled from Utah, Montana,   Northern California, Oregon, Washington… ASHLEY: Because of the decrease in daylight   and temperature, it triggers something in them  that makes them want to travel south, basically.

JESSICA: But not only do these genetic triggers  tell monarchs that it’s time to get a move on,   things start to change in the butterflies’ bodies.

They’ll start to do things like store more fat,   and slow down their aging.

This  allows them to live for 8 to 9   months—enough time to fly long distances  and survive as adults through the winter.

ASHLEY: We are really interested and basically  everyone wants to know where the monarchs are   going during their migration.

So, the best way  we can do that is to track individuals.

So,   to track individuals, we're using a  technique called radio telemetry.

And   it's actually been around for a really  long time to track a lot bigger animals.

Historically, even the lighter tags have been,  you know, 0.15 grams.

And for a butterfly,   even that is a lot because monarch butterflies,   even though they're one of the larger species in  North America, they only weigh less than a gram.

ASHLEY: These, on the other hand,   are incredibly light.

It's just a solar  panel that is connected to the tail,   which is basically its little antenna.

ASHLEY: If we can better understand how   individuals travel and they spend their  time in overwintering habitat on the coast,   we can better understand what kind of habitat  they need to complete their overwintering cycle.

JESSICA: Monarchs look for pretty specific  amenities during their winter vacation:   dappled sunlight, high humidity, access to fresh  water, and no freezing temps or strong winds.

ISIS: When monarch butterflies aggregate at  the overwintering site, they often form what   we call a cluster.

When the ambient temperature  starts to reach or exceed 55 degrees Fahrenheit,   monarchs are then able to utilize  their wing muscles and start flying.

They basically start rippling.

And you  start to see the flashes of orange and   black.

And then eventually one butterfly  will make the courageous decision to- to   leap out into flight, and then so  many will end up following them.

JESSICA: While it seems like clustering  might be about staying warm, it could   also protect them from storms and from  overheating.

That’s important both so they   don’t lose their fat stores too quickly,  and to maintain their suspended aging.

ASHLEY: One of the factors we think is  really important for determining where   monarchs like to cluster in a grove is wind.

We want to figure out what wind speed is a   threshold that starts breaking up monarch  butterfly clusters.

So, there’s a graduate   student from Cal Poly named Kyle Nessen,  and he put up sensors all around our grove.

KYLE: I'm going to check the batteries  right now and just make sure everything   is good to go.

And then once I'm done,  it will record the average wind speed   and the max speed every minute  for the next couple of months.

Right now I'm collecting actual wind measurements  throughout the grove at different points.

And then   the second half of this will be coming here  with a LiDAR drone and we’ll fly this whole   area with really high resolution 3D data and  recreate the forest structure in the computer.

JESSICA: That data could tell  researchers things like where   planting extra trees might create  a better spot for monarchs to hang.

JESSICA: There are plenty of mysteries we’re still  trying to unravel when it comes to monarchs, but   what we already know is that monarch populations  have fluctuated widely over the past decade.

JESSICA: In 2020, when the western  monarch population dropped to 2,000,   that seems like too much.

ASHLEY: They were close to what we would call  an extinction vortex, which is where there's so   few numbers that there's no way that they could  mathematically recover.

Luckily, we had a really   big bounce back and really good years.

If you  compare it to the population numbers we saw in the   eighties, we are still in a long term decline.

The  one good year does not necessarily make up for-   ISIS : Dozens of- ASHLEY: Decades.

Yeah many decades of not good years.

JESSICA: With a vulnerable population,  protecting habitat can be key.

Monarch   caterpillars have evolved to dine almost  exclusively on a plant called milkweed.

Milkweed contains toxins called cardenolides  that monarch caterpillars can sequester in   their bodies and retain as adults, a  defense against would-be predators.

They need these plants to  survive.

But due to habitat loss,   milkweed breeding areas are in  increasingly short supply.

That,   plus pesticide use, and climate change are  all big threats facing these butterflies.

ASHLEY: It's so great that we have monarchs in  our communities, but it's also pretty unfortunate   that where they choose to overwinter is on the  coast of California pretty prime real estate.

ISIS: The plain fact is that if we lose the  overwintering sites along the California coast,   we're going to lose the monarch migration as well.

JESSICA: We know more about monarch  populations perhaps than any other   type of insect that's out there.

And yet we  still don't really have enough information   to know the magnitude of what this kind  of massive drops and increases and drops   mean in terms of long term survival for  monarchs.

I think people should be worried.

But there are amazing efforts underway  to keep tabs on monarch numbers.

Isis   works with volunteers for  the Western Monarch Count,   a community science-driven initiative  that’s been collecting data since 1997.

ASHLEY: We're putting a lot of brainpower and  a lot of money into conserving habitat for   the monarch butterflies to try to save their  population.

I think we care because it's just   such an incredible phenomenon that a lot of  people feel a lot of emotional connection to.

ISIS: The declines in monarch butterflies,  especially on the West Coast, really   represent and reflect the declines of other  beneficial native insects and pollinators.

So,   our efforts to provide habitat  and protect habitat for monarch   butterflies is really benefiting  more than just these butterflies.

Monarchs have touched most of our  lives in one way or another.

So,   they really represent this symbol and  icon that can not only bring people   together over pollinator conservation,  but biodiversity conservation at large.

JESSICA: As you might imagine, for people  who live in the area where monarchs arrived   in tens of thousands of individuals, there was  a significant event that happened every year.

JESSICA: The monarchs’ migration to  the southwestern United States and   Mexico coincides with Día de Muertos  in early November.

To some people,   the butterflies represent the souls of  deceased loved ones who come back to   visit.

Preserving a species can help  us preserve cultural heritage, too.

So what can you do to help monarchs?

Well,  you can plant species of milkweed that   are native to your area.

You can plant  nectaring flowers for adult butterflies   to enjoy.

You can reduce pesticide use  and find a community science project in