Monarch migration endangered

February 2, 2014 • 2:39 pm

One of nature’s grand spectacles is the annual migration of monarch butterflies (Danaus plexippus), in which the insects travel from the U.S. and southern Canada down through the Great Plains to a small bit of forest in the mountains of Mexico, where they gather in a spectacular mass display comprising millions of breeding individuals. What is even more amazing is that the entire migration up and back doesn’t involve individuals of a single generation, but individuals from several successive generations (there is more than one generation per year). That means that the butterflies have some kind of internal, hard-wired drive to head south, generation after generation, eventually homing on the same small patch of Mexican woodland. Nobody has any idea how they do this.

That patch used to include 45 acres, but has been reduced through deforestation to about 1.6 acres. That, combined with bad weather over the last two years and the replacement of essential milkweed plants (the insects’ food) with agricultural plantings in the U.S., has severely reduced the populations of monarchs converging in Mexico. I’m not sure why the Mexican government hasn’t stopped this deforestation, as the gathering of monarchs is not only amazing to our eyes, but essential to the continuation of many monarch populations.  (For a longer discussion, see this article in the New York Times from Jan. 29.)

At any rate, reader Joe Dickinson sent in some pictures he took of another gathering place in the annual monarch migration, a spot near Santa Cruz, California. His notes:

Here are some non-avian wildlife shots.  A local paper recently reported that the famous muiti-generation migration of monarch butterflies is under serious threat due to environmental factors at both ends, so I went down yesterday to check one of the groves in Santa Cruz that is a southern terminus.  I did have the feeling a couple of weeks ago that numbers were down relative to two or three years ago (1st photo), but they looked pretty good yesterday.  One interesting puzzle:  I would think this complex migration has fairly deep evolutionary roots, but most roosting sites in the area are now in (introduced) eucalyptus groves.




39 thoughts on “Monarch migration endangered

  1. I understand that the main culprit in this story is the disappearance of milkweed plants resulting from increased use of Roundup herbicide.

  2. Great photos! I had about that msny on my honey maple tree about 7 years ago here near Toronto. By the time I had grabbed my camera they had flown away. I only saw them the one year. I think it was Fall, but might have been the return trip in Spring.

    1. I always have lots of milkweed in my backyard garden each year for the monarchs. Last year many of the milkweed plants were destroyed by Japanese Beetles.

  3. I’ve been a gardener for nearly 30 years, and just a couple of years ago I read a book by entomologist Doug Tallamy (Bringing Nature Home)that made me realize I’ve been doing it all wrong. So now my garden is transforming from all those prized imports to native plants, and I encourage other people to include as many native plants, including milkweeds, into their gardens. You can’t have native insects without native plants, and that includes many butterfly species, not just monarchs.

  4. Thanks, Jerry. For 40 years I’ve wondered about the line in The Beach Boys’ song ‘California Saga: California’ from the ‘Holland’ album: ‘There the monarch’s autumn journey ends on a windswept cypress tree’. D’oh, now I know what it means.


  5. 1.6 acres? I don’t know how you could possibly expect the migration to continue when all you leave them is 1.6 acres, regardless of how much milkweed is planted.

    People suck.

    1. There are actually a few different localitons along the coast. The main Santa Cruz location is Natural Bridges State Park, which is at about 10% population from what it was five years ago.

      Plant milkweed!

      1. The 1.6 acres refers not to the California roost, but the (formerly much larger) one in Mexico. Different migration routes, different populations.

      2. I often find more at Lighthouse Field than at Natural bridges. I believe there also is a site up by the UCSC Botanical Garden and, of course, down in Pacific Grove. Others?

        1. The campus of Cal Poly San Luis Obispo used to have a lot of monarchs in winter. They seem to pile up in scattered favorable sites along the coast. The presence of dense evergreens for shelter seems essential.

          Historically they probably used evergreen oaks, redwoods and Monterey pines, but eucalypts are obviously an acceptable (preferred?) substitute. None of those native evergreens provide nectar.

  6. Florida has, I understand, a non-migrating Monarch population. Comparing this year to the last few years here in Palm Beach County, the Monarch numbers look about the same.

    I always have milkweed in my tiny butterfly garden and two weeks after it is in the ground, it has usually been stripped bare by Monarch caterpillars — and sometimes by its fellow butterfly, the Queen, Danaus gilippus. When the leaves grow back, back come the Monarchs to lay eggs and the cycle continues year-round.

    Nevertheless, I can’t imagine the American Midwest without milkweeds and Monarchs along the roadsides.

  7. Fantastic photos.

    I read the title and thought that the royal family were moving! What a disappointment, they’re staying put.

  8. It strikes me as strange that no nature lover has considered buying the original 45 acres of Mexican forest to preserve the species? Probably for less than the annual salary of the average caring naturalist, the space would have been kept natural. Now, of course, the land would have to be restored to the old treed state.

  9. One of the greatest joys I have in my garden is watching the monarchs. I have quite a bit of milkweed that spreads itself quite happily all over. (I actively give it away to as many people as I can too.) In good butterfly years I have hours of summer entertainment watching them lay their eggs, caterpillars hatch and grow fat and wander away to do their thing. Followed by me crawling around to find the crysalis and wait for the emergence. The last few years have certainly brought fewer butterflies though. It must be amazing to see these migratory sites.

  10. The movie Flight of the Butterflies (2012) is absolutely terrific. It would show at Science Centers, although you can buy the DVD. It’s amazing to see on in IMAX theater in 3D. I’ve watched it at the Smithsonian National Museum of Natural History (NMNH) on my last two visits to DC. As Jerry said, the two generation migration from Mexico to Canada and the third generation’s migration back to one specific wintering spot in Mexico is a mystery. The ~40 year quest of scientist Fred Urquhart to find their winter hideaway and prove their migration pattern was inspiring.

    1. I’ll vouch for it, too. I saw it at the IMAX at the Milwaukee Public Museum (which has an excellent live butterfly exhibit, BTW).

      Good film.

      1. There’s also a novel, “Flight Behavior” by Barbara Kingsolver, that imagines the Mexican population showing up in Appalachia. I enjoyed it

  11. the entire migration up and back doesn’t involve individuals of a single generation, but individuals from several successive generations

    To clarify, several succeeding generations move steadily north, but individuals of a single generation make the long journey south. Amazing indeed.
    I’ve always thought that we’re going to have to figure out how behavior like this (and, as another example, species-specific spider webs) can be DNA-coded before we’ll have any chance at knowing how the mammalian brain works.

  12. I have on a handful of occasions seen monarch butterflies here in Geneva, in my garden when I was living in the countryside and in another place, also outside of town… and yes, there are some in Western Europe, from the UK to Spain, but they are quite rare.

  13. I read an article a year or two ago that claimed that the main culprit in the Monarch decline was the drought in the Southwest. Monarchs are being forced to try to cross hundreds of miles where there are few nectar sources. I have an old lady friend here in Illinois that has allowed milkweed to come up wherever it pleases in her yard and flowerbeds. She used to see quite a few Monarchs, but this last season never spotted one.

  14. My understanding is that the Mariposa Monarca Biosphere Reserve in Mexico is the wintering site for a huge part of the population from North America east of the Rockies. It is a terrifying thought that it is restricted to such a tiny area and one that is being reduced by deforestation.
    It seems vital that what remains is vigorously protected and I’d urge people to write to the Mexican Government via their Ambassador to request that they protect the species as strongly and effectively as possible. I understand WWF is working with the Mexican authorities and with local communities to achieve this.
    As has been pointed out, loss of its wintering habitat is not the only threat the species faces and it is also important to ensure that the larval food plant remains abundant as well as sufficient adult nectaring sources. Planting milkweed in gardens will no doubt help but I suspect will not be enough and measures to ensure more land is left untreated by herbicides to allow native wildflowers to grow are needed. It may prove difficult to bring about change of practices on farmland in this respect but other areas of land including road-side verges may provide opportunities.

  15. These insects appear to be quite common in New Zealand though what they feed on and whether they migrate I don’t know. Also, were they introduced?

    1. I believe they reached New Zealand unaided. Their ability to cross oceans is well documented and there are records of them turning up in the SW of the UK having crossed the Atlantic.
      I am not sure if they feed on any native plant species in New Zealand and it is possible that their establishment there depended on introduced milkweed species in gardens.

      1. From (they have a fan club here!):

        In NZ the natural food species of the Monarch (Danaus plexippus) larvae is the Asclepiadiae family – milkweed which includes swan plant (Gomphocarpus fruticosus) and giant swan plant (G. physocarpus) as well as Asclepias species such as tropical milkweed/bloodflower (A. curassavica). The tropical milkweed comes in two colours -scarlet (which has a gold centre) and gold (all yellow). The term ‘milkweed’ can be confusing – but a Fact Sheet on this is available. … Larvae in their latter stages can be also fed on a noxious weed which is sometimes called moth vine, cruel vine or kapok plant (Araujia sericifera), as well as cucumber, pumpkin and courgette – but only when they are ten days old or more than 2cm in length. This weed (moth vine) is on the banned list in some regions – check with your regional council. Adult butterflies will feed on any plant giving nectar. They usually choose flowers with bright colours, purples, pinks and blues. Hebes are very popular.

        Google is amazing…

        By the way, I know the moth vine only too well. It’s a creeper, grows like crazy over any trees, has huge seed pods, white sap which is a skin irritant. Altogether nasty.

  16. I live in western Oregon, and until the past 6 or 7 years, I could expect a few monarchs to pass through and nectar in my garden. And almost any roadside patch of showy milkweed would have a few larvae, and the surviving adults would no doubt return to overwinter on the central California coast.

    That migration is broken now, and I doubt that a few enthusiasts’ seeding of milkweed will bring it back.

    Still, the monarch is NOT endangered as a species. In fact,it’s opportunistically spread, having reached the Atlantic islands(accounting for the waifs in western Europe), and in Australia and Australasia in the past century-plus. Often said to fly across oceans, but more likely hitchhiking on ships.

  17. The novelist, Barbara Kingsolver, published a novel called Flight Behavior, which is based in part on the situation of these butterflies and the onset of global warming. There is a fairly sympathetic portrayal of scientists in it. A good example of art inspired by science….

  18. Off-topic…but, by this time in the morning, we’ve usually got a new Hili Dialogue as well as a couple other posts. Is Professor Ceiling Cat okay…?


  19. To clarify – the actual area of the overwintering preserves is much larger than these numbers given. The areas given are the total area within the preserves that is occupied by the butterflies. There are millions per hectare or acre, so they don’t try to count them all, but instead measure the area they cover. That has fallen from a peak of 21 hectares in 1996-7 (which would actually be more like 52 acres than 45) to this winter’s 0.67 hectares (1.6 acres). That is a 97% reduction in less than 20 years. So it is not a question of making the preserves larger, it is a question of raising more monarchs in the U.S., especially the “corn belt” from which half the migrating monarchs originate. Studies have shown that the majority of milkweeds in Iowa were historically in or next to cornfields, and with “Roundup Ready” corn, the increased use of Roundup herbicide has eliminated the large majority of previously available milkweed.

  20. I’ve had milkweed in my garden for five years but have had only a single monarch caterpillar in all that time. I see monarchs around. Not as many as I remember from years ago. Makes me sad.

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