Monarch Watch Blog

Monarch Population Status

Thursday, September 22nd, 2011 at 1:25 pm by Chip Taylor
Filed under Monarch Population Status | 11 Comments »

The following is a brief update on the status of the eastern monarch population.

The leading edge of the migration has now reached northern Texas. As many of you know, we attempt to follow the monarch population closely. Based on our experience, and ongoing data analysis of monarch numbers, we offer opinions/projections on what to expect in the near future based on our understanding of how the monarch populations have been affected by patterns of temperature and rainfall in the preceding months.

Late in the spring I started predicting a small migration this fall. In the Premigration Newsletter sent out with the Monarch Watch Tagging Kits, I predicted that overwintering population in Mexico would be similar in size to that of the low populations recorded in 2004 (2.19 hectares) and 2009 (1.92 hectares). It was clear that the monarch numbers in New England and recorded at Cape May would be low this fall, and that the numbers originating in the central region would be slightly better than those of the eastern Dakotas through Wisconsin but still low relative to long term numbers. The New England/Cape May projection appears to be correct as the numbers are down in this region. I was wrong about the central region (Ontario, MI, OH, IN, IL) – fewer monarchs appear to have been produced in this area than I expected. Wisconsin numbers also appear to be down.

The surprise is the eastern Dakotas and western MN. This area seems to be the source of a large number of the monarchs moving through the lower midwest at this time. Nevertheless, the overall numbers are down. But, it gets worse. The migration is just beginning to navigate a 1000 miles of hell – a nearly flowerless/nectarless and waterless expanse of central KS, OK, TX, and NE MX (see Drought Monitor).

Drought Monitor - 20 September 2011

It is too late for rains to change the situation in TX and northern MX. Monarchs will make it to the overwintering sites but their numbers will be significantly reduced by these conditions. My expectation is that that the overwintering numbers will be the lowest ever (previous low 1.92 hectares) and that the arriving butterflies will be in relatively poor shape with low fat reserves. If the average condition (mass) of the overwintering monarchs is lower than average, mortality during the winter could also be high. Other scenarios could include low returning numbers next spring with a reduced reproductive capacity due to low fat reserves. Keep your fingers crossed that there are no winter storms in MX that could make matters worse.

It will be interesting to see how monarchs cope with the lack of nectar and water as they move through TX. Monarchs, like most insects, have hygroreceptors (sense organs that are sensitive to humidity gradients); therefore, when conditions are extremely dry, we might expect monarchs to seek out the darkest and most humid habitats. If this plays out, most monarchs will accumulate in drainages, along rivers, move in an out of forests, and concentrate around other water sources.

As I pointed out in the Premigration Newsletter (and the August Population Status blog article), there is a new reality, or expectation, regarding the size of the overwintering population in MX. It now appears that winter populations will be in the range of 2-6 hectares (down from the long term average of 7.24) with 6 hectares being reached only during the most favorable conditions. In the near term, the average overwintering population will be close to 3 hectares. As we pointed out recently (Brower et al. 2011), the decline is related to the loss of habitat, particularly the rapid adoption of herbicide tolerant (HT) crops. The majority of these crops are planted within the summer (June-August) breeding area for the monarch population. In spite of weed control methods prior to 1996, when HT crops were first introduced, milkweed persisted in these croplands at a low level where they provided an excellent resource for monarchs. With the planting of HT engineered corn and soy followed by the use of glyphosate to control weeds, milkweed has been almost completely eliminated from these crops. At present, the total area of HT crops is larger than that of any state except TX and AK, or about 4 times the state of IL). The decline in the monarch population first became noticeable in 2004 when the percentage of HT corn and soy acreage exceeded 50% of all acreage for these crops.

Low monarch numbers in MX this winter and in the future means that the integrity of the overwintering sites is now more important than ever and that planting milkweeds in gardens and incorporating these plants in restoration projects either as seeds or plugs should receive the highest priority.

Monarch Waystations – Create, Conserve, & Protect Monarch Habitats

Bring Back The Monarchs – It’s not too late…

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  1. 11 Responses to “Monarch Population Status”

  2. By Shearl Spurlock on Sep 29, 2011

    I counted about twenty five Monarchs yesterday all where headed south,i live in Homosassa,Fl

  3. By Scott Waugh on Oct 9, 2011

    Just had to submit this since it was so unusual, I haven’t seen Monarch’s passing by for at least a month or two (probably more like two months). We’ve had one light frost about a week ago (in a string of wet weather that lasted a couple of weeks) – been warm and dry since then (and should be warm through this week).

    Saw two monarch’s today (10-09_2011) heading south – I wasn’t outside looking for them since I didn’t think I’d see any until the northward migration in 2012. I’m in Round Lake, IL (right up on the border with Wisconsin, 15 miles south and about 30 miles west of Lake Michigan.

    I told them they were late and wished them well, but they payed no attention to me and kept moving south. ;-) About half our trees have turned color or with a 1/3 of those already dropping leaves.

  4. By Susan Carpenter on Oct 13, 2011

    I spent Columbus Day weekend on the coast of Maine at Old Orchard Beach, just south of Portland. The weather was exceptional, 70s and 80s during the day, 50s at night. Almost no wind – perfectly clear skies. There was a steady stream of Monarchs heading down the coast all day, every day. More than I’ve ever seen before in all the years I’ve gone to OOB on the same weekend. There were also many along our route from VT to Maine – mostly nearer the coast though. Here in Central Vermont I haven’t seen any since before Columbus Day. But we had a bumper season here earlier.

    One fun note – as I was driving home from Maine I thought I saw a Monarch (or falling leaf) go right in front of my VW van. About 5 miles later I stopped for a light and off flew a Monarch from my grill. Seemed fine. Sadly I took it a little further north than it had been.

  5. By Scott Waugh on Oct 13, 2011

    Just wanted to add that my wife and daughter saw another Monarch the next day 10-10-2011, a day after I saw the other pair, when they were outside of our house in Round Lake, IL up near Wisconsin near Lake Michigan.

    The weather has been good for flying (today we got some rain) and its supposed to stay relatively warm for quite a while. Hopefully this late group can make it down.

  6. By Sondra on Oct 14, 2011

    Some Monarchs are passing over our house as I write this. It is not by any means a thick cloud of them, just a slow, steady movement of about one or two every 45 seconds or so.
    We’re in Spicewood, Texas, zip code 78669.
    So exciting!

  7. By Scott Waugh on Oct 15, 2011

    Here in Round Lake, IL on Oct. 14th. I was out playing tag with my daughter this morning and another Monarch came flying by which we followed briefly. The temp is about 54 degrees, but he / she appeared to have no trouble flying (lots of sun). It stopped to sample a dandelion flower and then moved on. Strong winds from the Northwest.

    The fact that I’ve seen 4 in the last week while being inside most of the time is really surprising, I wasn’t expecting anymore at this point. Maybe there’s a late pulse of them.

  8. By Hiedi Lambrecht on Oct 18, 2011

    I saw a couple of Monarch’s by the Mall of America in Minnesota over the weekend. I thought it was weird to see Monsrch Butterflies still in Minnesota. I thought they were crazy because it was so cold during that weekend. I told them that they shouldn’t be here and they just kept flying south, ingnoring me.

  9. By philip smith on Nov 23, 2011

    Last year I reared over 100 monarchs from cats to full flight.
    This year’s sole cat is feeding on parsley in my cage, as milkweed is long dead.
    I saw maybe 2 females in the garden all summer, after planting 40′ of new milkweed.
    It was a disaster for the mariposas this year…Is anything being done re; the ht problem?? Can the feds encourage anything?
    phil smith…Northeast Oklahoma..

  10. By Craig Wilson on Nov 23, 2011

    On November 21st there were over a dozen Monarchs floating over the USDA/ARS/SPA People’s Garden in College Station, TX which is also a Monarch Waystation. It was about 78 degrees F. and they landed to feed on nectar plants.

  11. By Ann on Nov 26, 2011

    We had at least 10 to 15 Monarchs each day during October and though the numbers are dwindling, we’re still getting a few now through our waystation. All look fairly strong and hungry. We’ve kept up a lot of nectar plants this summer and without a hard freeze yet the plants are flowering and feeding well. We’re in Carmine, TX 78932.

  12. By Audrey Burtrum-Stanley on Aug 2, 2012

    I am greatful to have this information on the Monarch. We keep careful tabs on all our favorite winged creatures at the National Buffalo River (Northwest Arkansas). All our friends in the area pay heed to the number of hummingbirds, light’n bugs and Monarch butterflies they spot during the warm seasons. With more care, we can educate and preserve these natural delights for future generations. Thanks for doing your part with this fine BLOG.

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