Monarch butterflies, and weird failures of observation

Photos: Wildlife-Friendly Garden and signage, © S Heard CC BY 4.0.  Monarch caterpillars on milkweed (in Minnesota), Courtney Celley/USFWS, CC BY 2.0.

My university, like many, is concerned with appearing green, and among its projects is a series of small plantings that offer (mostly) native plants with educational signage.  I pass by one of these every day on my walk to work: the “Wildlife-Friendly Garden”.  It has Joe Pye weed, roses, goldenrod, and a few other things, and it has some signs introducing passers-by to its “frequent visitors”.

One of the “frequent visitors”, we’re told, is the monarch butterfly: it has a lovely and informative sign.  This seems unremarkable: everyone loves monarch butterflies, everyone knows they’re common visitors to late-summer flowers like goldenrod and Joe Pye, and everyone knows they’re a species at risk* worth cherishing.  So how could I possibly have a beef with this sign?  Well, here’s the thing: my university is in Fredericton, New Brunswick – and we don’t have monarchs here. Or almost not.

Monarch butterflies, of course, are milkweed specialists as larvae (photo above the post).  Common milkweed, Asclepias syriaca, reaches its northern range limit very close to Fredericton (and in fact, its occurrence here probably represents a fairly recent range expansion as a result of habitat alteration by humans).  Unsurprisingly, where milkweed comes to a range margin, so does the monarch butterfly (and the rest of the specialist milkweed-feeding fauna too).  In Fredericton, I see on average one adult monarch butterfly a year.  I’ve never seen a caterpillar here, suggesting that our occasional adults are probably storm-blown or otherwise casual visitors.  We aren’t terribly far from places with more monarchs – there’s a long-running study tagging migrating monarchs about an hour’s drive south – but the near-absence of local monarchs is nonetheless consistent.

And yet: the “frequent visitor” sign for monarchs is no outlier.  Our local newspaper regularly prints exhortations to plant milkweed for monarchs; elementary schools plant and celebrate these milkweed gardens, and rear and release monarchs from farmed pupae; and I frequently hear members of the public talking about monarchs as if they were common members of our local fauna.  In fact, I’d wager that people “remember” seeing monarchs in their gardens, despite the fact that such sightings are almost certainly imaginary. This is a fascinating failure of observation.  Monarchs are common in public discourse and in people’s media experience, and so people just assume they’re common in their direct experience too – even if they aren’t.

This has always bugged me about monarchs.  But I make the same failures of observation myself; and I bet you do too.

I was thinking about this after getting reviews back on a recent manuscript.  One reviewer suggested that we were remiss in not citing the extensive literature that establishes point X.  I was actually quite pleased to get this criticism, because point X really would have been stronger with citation.  So off I went down an internet rabbithole searching for that literature.  Guess what?  No such thing.  And I could be annoyed by this, but I know that more than a few times, I’ve been on the other end of this exchange.  Usually, it’s when I suggest to one of my grad students that some point in their paper merits a citation, and I say “there are lots of papers about this”.  And sometimes I’m right – but sometimes, I’m very, very wrong.

There are things we all know, and we presume that the reason we know them is that we’ve read papers saying so.  As scientists, that’s generally how we know things, right?  But sometimes, these things we know turn out to be just things we think we know.  As a concrete example, I’ve been told a million times that insect herbivores can reduce performance of individual plants, but don’t impact plant population dynamics.  I’ve lost track of the times someone has told me about the literature that supports this contention.  The thing is, it doesn’t exist.  Everyone thinks they’ve read papers demonstrating that herbivores don’t influence plant populations, but those papers are as imaginary as the Fredericton monarchs.  In reality, nobody studies the question because we all think we know the answer; but we don’t know the answer because nobody studies the question**.

Failures of observation: imaginary monarchs, imaginary papers.  We let things everyone says and everyone takes to be true override our own (lack of) observation.  It’s a funny failing for scientists, who are supposed to favour evidence above all else.  But then, scientists are just people, and when we aren’t deliberately vigilant, we do what people do.  It will be good for me to think about this each time I pass the monarch-less Wildlife-Friendly Garden.

© Stephen Heard  November 28, 2017


*^Largely due to issues with their overwintering range in Mexico, not with the availability of larval and adult resources in their summer range, but that’s another story.

**^There’s some literature-review support for my argument in this paper, but I’ve been meaning to write a blog post fleshing it out.  Some day…

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6 thoughts on “Monarch butterflies, and weird failures of observation

  1. Peter Apps

    I suspect that the Bellman’s rule applies; what I tell you three times is true. Something gets repeated a few times, then that gets cited a few times and methods are adopted to take it into account, and before you know it a whole subject has gone down a blind alley; APPS, P.J. 2013. Are mammal olfactory signals hiding right under our noses ?. Naturwissenschaften 100: 487-506.https://www.researchgate.net/publication/236837171_Are_mammal_olfactory_signals_hiding_right_under_our_noses

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  2. Macrobe

    Personal observations may not always align with collective observations. Several Canadian visitors (including from Quebec) to the refuge where I worked last summer (monarch program coordinator) gleefully reported seeing flying/nectaring monarchs and a few scattered larvae. Monarch dispersal range is changing and expanding northward, sometimes when and where their resources are scarce (mismatched phenology has been documented throughout North America). Generational and density changes linked with this northward expansion has been documented, but whether this is a true trend or not remains to be proven. Two studies modeled and forecast changes in both Asclepias and monarch butterfly ranges with climate change (Flockhart, et. al., 2017 and, most notably, Nathan Lemoine, 2015). You may see more monarchs in years to come. 🙂

    Your footnote regarding the population decline -“largely due to issues with their overwintering range in Mexico, not with the availability of larval and adult resources in their summer range, but that’s another story.”- echoes the ongoing controversy. I presume you are referring to the studies published in September 2015 issue of Ann. Entomol. Soc. Am. At least half a dozen published papers since then have challenged the source data sets and conclusions of those studies. Because of the monarch’s migratory nature and the complex spatio-temporal breeding dynamics, multiple factors impact their population status. We could apply Liebig’s Law and cite only the weakest link in their complex life cycle, but too many links are weak. This isn’t a binary issue.

    Two most recent papers that help elucidate weak spots in the former studies: Pleasants, Zalucki, Oberhausen, Brower, Tayler, and Thogmartin. 2017. PLOS One, 12, “Interpreting surveys to estimate the size of the monarch butterfly population: Pitfalls and prospects”; and Marini and Zalucki, 2017. Scientific Reports 7, “Density-dependence in the declining population of the monarch butterfly”. What is sorely needed in the monarch research community is a central database and archive, including data of all life stages. Until then, we may still bicker back and forth while monarchs continue to struggle.

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  3. Elizabeth Moon

    On monarchs between Mexico and central-northern US states. We live in central Texas, about 50 miles north of Austin. We usually see monarchs in migration at both ends–heading north and heading south. Monarchs heading south can nectar on many things besides milkweeds, though we often have some late blooming milkweeds (small and scruffy, not sure of species) in the fall. But monarchs heading north need milkweeds to reproduce–and they need them at exactly the right time. When we first moved here, in the late 70s, the northward moving monarchs found a lot of “Antelope Horns” milkweed (Asclepias asperula), the earliest to bloom here, followed by “Green Antelope Horns” (Asclepias viridis) and every early spring offered opportunity to photograph monarchs on these plants out in open pastures.

    Climate change since about the mid-1990s has had two effects deleterious to monarchs in migration passing through this area. (So has land development with the growth of Austin but that’s a different problem.) Milkweed abundance at the time of peakj monarch migration has diminished–partly from changes in the time of flowering, and partly from the effects of heat and drought on the existence of those two species. A. asperula blooms earliest, but the population was devastated by a severe five year drought from about 2008 to 2013. A. viridis blooms a few weeks later, with a longer blooming period and stands taller off the ground (still low) but its population was also much reduced by drought. This was true not only on our land, but in neighboring open land. I can’t prove the effect on the northbound population, but the drought was widespread across Texas and extended more of the Southwest.

    Are there any studies of the timing of various milkweed species with the arrival of monarch migrants on the way north? I don’t know. But there needs to be. We do not have “common milkweed” at all. We have at least four other species of milkweed on which monarchs and their larvae might feed at times (though mostly either A. asperula or A. viridis that I’ve seen.) We also have the “milkvines” (relatives but not milkweeds).

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    1. Macrobe

      If Stephen does not mind, I can answer some of your questions, Elizabeth. What you are describing is ‘mismatched phenology’, where the life cycles of the resources an animal requires to subsist become out of sync when and where the animal needs them. This is increasing for many species in both North America and Europe. Monarch butterflies are only one of several species experiencing mismatched phenology.

      An example of this phenomena occurred last summer in most of the northeastern states that experienced an extreme drought. The most prevalent milkweed (A. syriaca) had emerged, bloomed and senesced a month early. It was not a resource that reproductive monarch females could utilize for breeding when they migrated to that area. Fortunately, the A. incarnata (swamp milkweed) emerges and blooms later (and longer) than the A. syriaca. This species of plant was the dominant native species that was used for reproduction last year in many areas of the northeastern states.

      Some species can adapt to these changes. Birds have more success than some invertebrates and mammals. Because the monarch is a specialist during the breeding stage of their life cycle, as Stephen mentioned, they absolutely require Asclepias species to regenerate. However, they can migrate to other areas that may have the resources they need. The important issue is that the lifespan of the adult after they leave their winter roosts is short-lived. Their sole mission is to find milkweed plants and deposit their eggs. Considering that they have survived for five months with barely any nutritional intake, you can see why this drive is so important. That is why milkweed resources in Texas, especially southern TX, are important. These remigrants are the sole source of the first generation larvae in North America.

      Availability of breeding resources in Texas and southern Oklahoma is a top concern of the monarch conservation community (as evidenced by its priority status in the Monarch Conservation Implementation Plan (Monarch Joint Venture)). The challenges are climate change and habitat destruction. Increasing habitat for both nectar and breeding resources is imperative for monarchs migrating south and north.

      A few resources you may find helpful to learn about the phenology of milkweeds in your area are the Xerces Society, The Lady Bird Johnson Wildflower Center, and Journey North. The latter is a Citizen Science project to map movements and timing of not only migrating species (Including monarchs), but also milkweed, throughout the US and Canada. If I recall, Texas A&M has a thorough publication on all the known Aslepias in Texas.

      Two wildlife refuges I have worked with have an ongoing program to survey and document the phenology of native milkweed and monarchs on their refuge. This year, the refuge survey in New York included phenology of milkweed and monarchs throughout the entire state. We hope to use this long term data to track patterns and trends in both Asclepias and monarchs. A refuge in New Mexico has also begun a similar program, with preliminary data from last year. You can also search the data archives at Journey North for both Asclepias and monarchs for past year’s data.

      Additionally, you might also visit (if you haven’t already) the USFWS Balcones Canyonlands Wildlife Refuge. I know they have implemented a monarch and breeding survey there this year. They have more local information for you.

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  4. Laura

    Hi, I’m not a scientist and I know little about monarchs, but I was struck by the truth of the observation “what we think we know” versus “what we actually know”. I used to be a counselor and people’s misconceptions were a huge part the difficulties they experienced in life. Finding the reality (of whatever the situation) was generally the most enlightening thing for a person.
    Just a comment! No citation.

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