A Toast To Bats That Pollinate Agave, And Tracking Monarchs

How bats, agave plants, and tequila are connected. Plus, tiny trackers on monarch butterflies reveal their migration journeys.

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Ira Flatow?

  Science Friday is supported by MathWorks, creator of MATLAB and Simulink software for technical computing and model-based design. MathWorks, accelerating the pace of discovery in engineering and science. Learn more at mathworks.com.

• 0:19Ira Flatow?

  I'm Ira Flatow, and this is Science Friday. Today on the podcast, we look at two marvels of a migration in Mexico. We'll hear how researchers use tiny tracking devices attached to individual monarch butterflies to record their epic voyage south. But first, how the dietary needs of a migrating bat influences what ends up in your margarita glass. Okay, let me explain. When you think about bats, chances are you think of the ones you see at dusk flitting about to hunt insects, right? But some species of bats like to eat fruits or flowers, not bugs, and they play an important role as pollinators.

• 1:03Ira Flatow?

  Now, one place that the pollinator role is crucial is in the relationship between bats and agave plants. And that has consequences both for the ecosystems around the agave and for your liquor cabinet, since agave is the source of drinks like tequila and mezcal. Now you get it, right? Well, here to explain this seemingly strange connection is Dr. Kristin Lear, Director of the Agave Restoration Initiative at Bat Conservation International. Welcome to Science Friday.

• 1:34Speaker 01

  Hi there. Thanks for having me.

• 1:35Ira Flatow?

  You're welcome. What kind of bats are we talking about here?

• 1:39Speaker 01

  So there's three species of nectar-feeding bats that we're talking about that migrate between Mexico and the US and that feed on the nectar of agave plants. Unfortunately, one of them is endangered, the endangered Mexican long-nosed bat, and that's why we're working to protect them.

• 1:56Ira Flatow?

  All right. So explain to me the connection between the bats and the agave.

• 2:00Speaker 01

  Yeah, so these bats, the three species are migratory. They mate in central Mexico, and then the pregnant females, while they are pregnant, they undergo a long-distance, over 700-mile migration northward up to northern Mexico and the US southwest. And along that route, they're feeding on these beautiful blooming agave plants that have these nectar-filled flowers that provide the fuel for this migration. And then, once those pregnant mothers reach northern Mexico and the US, in some areas, it is only agave plants that are available and providing nectar

• 2:41Speaker 01

  for these bats and for these mothers to sustain them and help them feed their babies.

• 2:46Ira Flatow?

  Yeah, and so I guess it's critical for the survival of the plants then, too.

• 2:51Speaker 01

  Yeah, yeah, these bats are, as they're feeding from the agave flowers, they're kind of these clumsy flyers when they go up to the agave flowers, and they kind of clumsily fall onto the flowers and they get covered in pollen. And then they spread that pollen over miles between different agave plants. These bats can fly 50 kilometers or more one way from a roost at night to go feed and then go back to their roost. So they're really spreading that agave pollen across those different agave populations and really helping maintain the genetic diversity of those plants.

• 3:27Ira Flatow?

  I would have never thunk that a bat is a pollinator.

• 3:32Speaker 01

  They're kind of the overlooked pollinator, you know, because they're out at night. We get to see butterflies and bees and hummingbirds, you know, during the day, but these bats are kind of this mysterious, unknown pollinator just because they're out at night and we don't get to see them.

• 3:46Ira Flatow?

  So can the agaves reproduce without the bats?

• 3:50Speaker 01

  Some agave species also reproduce asexually. So through rhizomes, for example, under the ground, they have these little pups or baby agaves that grow out from the mother plant. But some species of agaves only reproduce sexually through pollination and seed production. So you have a mix, and even for the ones, the agaves that can clone themselves or reproduce with pups. If you're a clone, you're genetically identical to the mother plant. So if if you clone too much over time, that population of agaves is too genetically similar and bad things can happen. Pest outbreaks, disease outbreaks can come through and wipe out that agave population because there's no genetic diversity to protect them.

• 4:36Ira Flatow?

  So as we're drinking our tequila drinks, we should know that without flowering agave, we would have no tequila or mezcal?

• 4:43Speaker 01

  Correct. Yep, these bats and these agaves have evolved together. And without those bats, we would not have those lovely products that we so enjoy.

• 4:52Ira Flatow?

  We should hoist one, right? While we're drinking and

• 4:55Speaker 01

  We should.

• 4:56Ira Flatow?

  Toast the bats.

• 4:57Speaker 01

  We definitely should.

• 4:59Ira Flatow?

  I'm gonna remember that. So you see, you want to be nice then to your agave plants. What are the threats? What is threatening their lives?

• 5:07Speaker 01

  Yeah, so so, you know, we you just mentioned harvest of agaves for liquor like tequila, mezcal, bacchanara. That can be done unsustainably or sustainably. So, you know, depending on how it's done, can either support bats or not support bats. But beyond, you know, direct harvest of agaves, there are other big threats to agaves like grazing. Cattle love to eat the the growing stalks of the agaves because they're really full of sugar and they're really kind of a treat for the cattle. So in places that have kind of this unsustainable grazing, these these cattle are are eating the agaves. And they're also kind of getting rid of the the natural native grasses that sustain agave populations.

• 5:52Speaker 01

  So grazing, land use change in general, expansion of agriculture, and then drought. Drought is a big thing that's impacting a lot of ecosystems, including agaves. Agaves are pretty drought tolerant, but you know, when you have extreme drought for extended periods of time, that's leading to losses of agaves and leading to things like wildfires that also

• 6:16Ira Flatow?

  Wow, climate change.

• 6:18Speaker 01

  Yeah, it's all tied, it's all exacerbated by that.

• 6:21Ira Flatow?

  I know that you're trying to help the bats by restoring the agave. But beside the relationship with bats, why is agave so important?

• 6:32Speaker 01

  So at Bat Conservation International, we're working to restore these agave plants through the Agave Restoration Initiative. Of course, our angle is the bat angle, right? We want to save these bats. But agaves are so important economically, right? For tequila, mezcal, black nora, all these products that we get, agave syrup that we can buy at the grocery store. They're this really important economic product, but they're also culturally important in many communities in Mexico and in the US. They support erosion control. So if you plant an agave, their root systems help sustain the soil and help maintain healthy lands and healthy soils. There's many other uses, medicinal uses for

• 7:15Speaker 01

  agaves. Cattle fodder, you know, you can chop up agaves and feed them to your cattle and goats, especially in times of drought when there's no natural, you know, grass fodder out there. So, you know, all of these reasons are reasons that people want to protect and restore agaves besides just protecting the bats.

• 7:34Ira Flatow?

  Okay, so give me your pitch to the people living on or near agave land for why they should protect the agaves. Is it money? Is it the environment? Or everything or all of that?

• 7:45Speaker 01

  Yeah, I mean, all of it. But I really think it comes down to what's your angle? What is driving you? You know, we all come at conservation or land restoration from different angles. Say you're a person in the US. We work with a lot of private landowners in the US or community groups. They love agaves because they're beautiful plants. They're iconic desert and grassland plants. So they want to plant and restore agaves to beautify their landscapes. That's one angle. Or if you're a cattle rancher in Anahito in Mexico, we work a lot with communities in Mexico, you want to have sustainable food,

• 8:24Speaker 01

  fodder for your livestock. Planting agaves and restoring the land helps you feed your livestock and maintain your livelihood. And then, you know, then there's the crazy bat nerds, the bat people who want to save the bats, right? I think we all come at it from a different angle, but we all get to the same goal.

• 8:41Ira Flatow?

  Yeah. Speaking of saving the bats, are there things people can do to help the bats? Like building bat boxes?

• 8:48Speaker 01

  Yeah.

• 8:49Ira Flatow?

  Things like that?

• 8:50Speaker 01

  Yeah. So some species of bats do roost in bat boxes or bat houses. Um, these three nectar feeding bat species do not roost in those bat boxes, but other species do. So in cases where there's habitat that's being destroyed or you're doing like an exclusion of bats from your house, that would be a great time to put up a bat house, um, to help, you know, provide a shelter for them. But also one thing you can do anywhere you live is plant a bat garden. You can plant night blooming flowers, agaves, of course, if you're in an agave area, you can plant agaves. But even if you're not, you can plant native night blooming flowers

• 9:31Speaker 01

  that open at night and attract nocturnal insects that our insectivorous bats can eat. So you have your own little kind of bat buffet, bat smorgasbord in your garden and you're supporting bat populations by planting a bat garden.

• 9:45Ira Flatow?

  That is cool. All right. So how, how has the restoration effort been going? Can you, can you track the progress?

• 9:51Speaker 01

  Yeah, it's been going great. So we have been working on the agave restoration initiative for about seven years now. And we have planted a little over 180,000 of these agaves across that bi-national migratory corridor. We have over a hundred partners that we work with in the US and Mexico, including ahito communities, private ranchers and landowners in the US, tribes, government groups, NGOs, et cetera. We kind of run the gamut. And we're also not just planting agaves, we are. We're restoring the land, so we're working with communities to implement sustainable grazing and management practices.

• 10:34Speaker 01

  We support community green business enterprises that support native habitats. And all of this together is helping to restore that bi-national nectar corridor.

• 10:44Ira Flatow?

  So you're hopeful that this is working. Your effort is making a difference with all these problems.

• 10:48Speaker 01

  Yes, we also monitor the roosts of these bats, you know, where they're they're living. And we are seeing the numbers starting to stabilize for the endangered Mexican long-nosed bat. So there there is hope that that what we're doing is working and that what we're doing will continue to support these bats long into the future.

• 11:05Ira Flatow?

  Well, I want to thank you very much, Dr. Lear. I will never look at my drink again the same the same way. Thank you for taking time to be with us today.

• 11:16Speaker 01

  Absolutely, thank you. And yeah, next time, just raise your glass to the bats.

• 11:19Ira Flatow?

  I'll be doing that, I hope. Dr. Kristin Lear, Director of the Agave Restoration Initiative. That's at Bat Conservation International. She is based in Loveland, Colorado.

• 11:35Ira Flatow?

  After the break, the tech that lets researchers keep tabs on butterflies on a thousand-mile voyage and what they're learning from that flight data. Stay with us.

• 11:49Speaker 02

  Science Friday is supported by PBS, presenting Going Wild. If you love learning about the natural world and meeting the scientists who help us understand it, be sure to check out the new season of Going Wild with Dr. Ray Wynn Grant. It's the chart-topping and Webby Award-winning podcast from the folks at Nature on PBS, now with a video companion series. In this season of Going Wild, host acclaimed wildlife ecologist Dr. Ray Wynn Grant heads out into the field to explore the animals, people, and stories that make nature worth saving. Stops include a hibernating black bear den in Arkansas and an underwater shipwreck site off the Florida coast. If you're looking for a place to start, check out the season's debut episode, where Ray joins beloved biologist and influencer Jordan King in the Florida Everglades to learn about

• 12:34Speaker 02

  his unlikely journey into science and how to study a wetland when it's not very, well, wet. So don't miss out. Follow Going Wild with Dr. Ray Wynn Grant on Apple Podcasts, Spotify, YouTube, or wherever you get your podcasts.

• 12:47Speaker 03

  Support for Science Friday comes from the William K. Boz Jr. Foundation.

• 12:55Ira Flatow?

  Turning from bats to butterflies, by now, the annual fall migration of monarch butterflies is over. The eastern population has moved to central Mexico to overwinter, and the western population has camped out in coastal California. That migration can mean a flight of thousands of miles, which makes you wonder, how in the world do monarchs do that? Joining me now is science journalist Dan Fagan. He's author of a recent article in the New York Times detailing how researchers are tracking individual butterflies as they migrate. He's also director of the Science Health and Environmental Reporting Program at New York University. Welcome to Science Friday.

• 13:36Speaker 04

  Thanks, Sarah.

• 13:37Ira Flatow?

  Okay, so how do you go about tracking a single butterfly?

• 13:41Speaker 04

  Well, we really couldn't do it until very recently. Or I guess it would be more accurate to say that we've done it in very primitive ways for many years. It used to be that all you could do was put a sticker tag on a monarch and hope someone would find it, look at the number on it, and at least know where that monarch came from. There's now a technology that creates a radio tag that's small enough that can actually be glued to the thorax of a monarch butterfly. And for the first time, we know not only where these journeys start and end, but we know everywhere that monarchs go in between, and it's pretty amazing.

• 14:22Ira Flatow?

  You mean it's small enough that it doesn't load down the butterfly so it can't fly?

• 14:27Speaker 04

  Well, we know that monarchs can fly with these tags. It surely affects them somewhat. But we've had tests of monarchs flying all the way from as far as Ontario, and they've been tracked all the way to Mexico. So at least some of them, a significant percentage of them, are not affected by the tags, at least not to the point where it prevents them from migrating.

• 14:53Ira Flatow?

  Okay, so you have these little radio transmitters, right, on each of the monarch butterflies? And how do they transmit? Who picks them up?

• 15:02Speaker 04

  That might be the coolest part. They're solar powered, right? So there's not a big, heavy battery that the monarchs need to carry. But what's most interesting is that the information gets continuously downlinked, I guess you could say, to anyone who has a cellphone that is Bluetooth enabled. As long as your cellphone is on, you are helping to track these butterflies.

• 15:28Ira Flatow?

  That's how those little iPhone tags work also, don't they?

• 15:32Speaker 04

  Correct. It's how your Find Your Phone works. So as a result, there are literally billions of potential monitoring stations for these tags. And you can get very robust data. It's not perfect data. There are still spots that are not well-covered, but there are so many Bluetooth-enabled cellphones that there are not very many of these dead spots. In fact, some of the monarchs have even been tracked over the ocean because they come close enough to a passing boat, for example.

• 16:09Ira Flatow?

  No kidding. All right, so now that they've collected all this data, have they found anything surprising about the migrations?

• 16:16Speaker 04

  Yeah, I had a good conversation with Chip Taylor, who's the founder of Monarch Watch. And Chip was very surprised by some of the things that these paths show. For one thing, monarchs get blown way, way off track. And yet, in many cases, they have the ability to right themselves and eventually head south again. And Chip, for one, was surprised by just how drastically they can get blown off of their general southwestern course. So that's one surprise. I think another one is that, you know, there's been a lot of controversy over how many of these monarchs really make it.

• 17:00Speaker 04

  We know that a lot of them don't. There are so many perils along the way, and it's very exhausting for them. They have strong wings, but... It's a lot to ask them to fly thousands of miles. And yet, judging from these tag monarchs, we have about 400 so far that have been tracked this year, a pretty decent percentage of them make it down to the Mexican sites. So in some ways, that's good news. It suggests that more of these monarchs can survive the journey maybe than many experts thought.

• 17:35Ira Flatow?

  I guess finally, what is the problem that these tag flights are trying to solve?

• 17:40Speaker 04

  Generally speaking, the migration is this wondrous, amazing thing. And it's, you know, people have a real emotional connection to this butterfly. They've grown up with it. Its habitat is most of North America during the summer. So they love it. And yet, this migration is certainly in trouble. We know from measuring the size of the Mexican colonies that there have been drastic reductions in the numbers of monarchs that make it all the way to Mexico and thus are able to continue their yearly, multi-generational life cycle. So we really need to understand what's happening on these migratory paths if we want to save

• 18:25Speaker 04

  the migration itself. Because there are serious questions, Ira, as to whether we will see migrating monarchs 20 years from now, 30 years from now.

• 18:39Ira Flatow?

  What a shame that would be.

• 18:41Speaker 04

  Yeah, it really would be. I mean, people love this butterfly. And if we want to make progress in protecting it, we need to really understand its migration much better. And until now, until this year, the paths that monarchs took were almost a complete mystery. And now we know, after a century of studying monarchs, and it's really quite amazing.

• 19:03Ira Flatow?

  Wow, thank you, Dan. This has been quite fascinating. Thank you for sharing what you found out about them.

• 19:09Speaker 04

  Thanks. It was good to be with you, Ira.

• 19:10Ira Flatow?

  Dan Fagan, science journalist and director of the Science Health and Environmental Reporting Program at New York University. And you'll find a link to his article on the butterfly migration, all there on our website at sciencefriday.com/monarch.

• 19:33Ira Flatow?

  This episode was produced by Charles Berkquist. I'm Ira Flatow. Thanks for listening.