Dr. Karen Oberhauser: Monarch butterflies under threat

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KAREN OBERHAUSER: I’m Karen Oberhauser. I’m the director of the University of Wisconsin-Madison Arboretum. And since 1984, I’ve been studying monarch butterfly conservation and biology. And now I spend a lot of time on bigger-picture conservation and education and land care issues.

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KAREN OBERHAUSER: Let’s start with now—what’s going on with the monarchs now. So, if we start with monarchs now, in—throughout the United States, monarchs are mostly in the northern half of the country and into southern Canada. These monarchs will produce another generation. And the next generation will migrate to their overwintering site. So, they’ll migrate south. And the monarchs west of the Rocky Mountains will migrate to sites along the coast of California. And monarchs east of the Rocky Mountains will migrate to sites in central Mexico. So, those monarchs start leaving—that next generation of monarchs will start leaving their breeding grounds in mid-August and start arriving at their wintering grounds in late October and early November. And then those very same monarchs will stay in their overwintering grounds until about mid-March, next spring, and start moving northward. And they will lay eggs and produce a new generation of the year in the southern part of the United States. And those offspring—so the new generation—will move into their northern breeding grounds and go through 2 to 3 non-migratory generations over the course of next summer. And then the cycle will start again.

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KAREN OBERHAUSER: So, while monarchs are spread out over large areas during the breeding and migratory portions of their life cycle, of their annual cycle, they’re concentrated in the winter. So, this is how we usually assess how the population is doing, is we monitor them in the wintertime. And for the California or the western population, people actually count the numbers of monarchs hanging in the trees. They count individual monarchs. And those numbers range from—one year, they were under 2,000, so that population was very low. And some years, they’re up to about a million. And in the eastern part of the United States—for the eastern migratory population, we really can’t count individual monarchs because there are just too many of them. So, we measure the area that’s covered with trees, covered with monarchs. And that area has ranged, over the time that I’ve been studying monarchs, from a high of about 18 hectares—a hectare is a little over two acres—to a low of under one hectare. So, that means during that low year, all of the monarchs from the eastern part of the United States fit into an area about the size of a football field.

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KAREN OBERHAUSER: We see a lot of variation from year to year, and a lot of that variation is weather-driven. But if we look at the trend for—especially for the eastern population where we have comparable numbers since the early 1990s, numbers are generally going down. What I like to do is look at decade averages. If we look at the last decade, the average area occupied was under three hectares—about 2.6 hectares. If we look at the previous decade, it was almost six hectares. And before that, it was over nine hectares. So, while there’s a lot of year-to-year variation, the general trend is downwards. That’s similar for the western population. There’s been a general downward trend. Numbers for both populations last winter were up a little from the previous winter, actually up quite a lot for the western population and up a smaller amount for the eastern population. So, we do still see a lot of annual variation but a general downward trend.

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KAREN OBERHAUSER: The most important things that affect the numbers of monarchs that we see in any given year are the amount of habitat available to them. And that has generally been decreasing, although we’re probably holding our own right now. There’s still some loss of habitat going on. But there’s also—a lot of people are increasing the amount of habitat available. So, we know that habitat loss during the breeding season is associated with this downward trend. And we also know that weather is associated with numbers of monarchs. So, there are good monarch years and bad monarch years. A good year has kind of average temperatures and precipitation. Hot, dry years aren’t good for monarchs and cold, wet years aren’t good for them. But that’s kind of like the Goldilocks theory of monarchs, that they do better when it’s not too hot and not too cold and not too wet and not too dry.

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KAREN OBERHAUSER: It really is dependent on the region. So, in the northern part of the breeding range, conditions are actually getting better for monarchs because a little bit warmer up there is actually better for them. But in the southern part of their summer breeding range, it’s getting too hot. And so, we’re seeing increases in temperature. We’re seeing—and this varies from region to region—but we tend now to have big rainstorms, and the rain tends not to be spread out so much. So, we kind of go from wet conditions to dry conditions in a lot of summers, and that’s harder on them. And so climate change is, in large parts of their breeding range, making it too hot and often too dry for them.

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KAREN OBERHAUSER: Well, there are lots of citizen science projects out there that people can join. And depending on where they live and how much habitat they have available to them, there is a project they could do. So, one that’s a very easy project to join is called Journey North. People just report the first monarch they see in the year, and we can watch the monarchs move north. We can compare where they move from year to year. We can see how that movement is dependent on weather and habitat availability. So, that’s something where you just see a monarch and report it. It’s very easy. So, Journey North is a great one.

If people are interested in more detailed studies—for example, of the fall migration—they can join the Monarch Watch Tagging project where they get little stickers. If you look at probably the—your index finger, the sticker is about the size of the fingernail on your index finger. And those stickers go on the butterfly wings, and we can actually track individual monarchs. If somebody puts a tag on a monarch in the northern part of their breeding range and then the tag is recovered further south, we know exactly how far it flew in a given amount of time.

For more detailed projects, there’s something called The Monarch Larva Monitoring Project, which we run out of the University of Wisconsin Arboretum. That project involves going out to a habitat every week and looking at a known number of milkweed plants and counting the number of eggs and caterpillars that people see on those milkweed plants. They can also collect adult monarchs and put a little piece of tape on the abdomen of the adult monarch and check to see if it has a protozoan parasitic disease, and that’s a program called Monarch Health that’s run out of the University of Georgia.

So lots and lots of opportunities to help study monarchs. And also, people can just join projects where they’re looking at all butterflies. There are lots of butterfly monitoring programs. A lot of states have butterfly monitoring networks. There’s a program called the North American Butterfly Association that does butterfly counts every summer. So, those are great because people are looking for all monarchs and we—or all butterflies, and we can pull out their monarch numbers. So, lots of ways that people can collect data to help us learn more about monarchs.

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KAREN OBERHAUSER: Besides getting involved in citizen science, which is a direct involvement in studying monarchs, there are three big things that people can do. And one is to increase the amount of habitat that’s available to them. And this can be in people’s yards, if they have more land available. They can do it at their place of work or their church or their kids’ school, anywhere that there’s land available to put in habitat. The nice thing about monarchs is they don’t need a lot of habitat. It’s not like we’re trying to protect habitat for spotted owls or wolves. Monarchs can find a milkweed plant in a crack in a sidewalk. So, planting milkweed is really important. That’s the only host plant that monarchs can eat when they are caterpillars. But there are many kinds of milkweed, so you can have a beautiful garden with a lot of milkweed in it. And they also need nectar plants. So, those are the two things that are important for the monarchs to include in any habitat.

People can also support organizations that are supporting habitat. So, if you have a local nature center or large national organizations, nature conservancy—any organization that’s working on habitat conservation. And finally, because monarch conservation will really take all of us working together, people should spread the word. So, when they learn a little bit about monarchs, they should tell as many people as they can about monarchs and get their friends and their neighbors and their kids and their grandkids and everyone else involved as well.