[Native Gardening] Monarch Butterfly Population Status

 



Monarch Population Status - September 2011
by Chip Taylor - Director, Monarch Watch

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 at
http://droughtmonitor.unl.edu/).

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.

So what can you do?

- Pledge your support of Monarch Watch via our 2011 fundraising
campaign (3 days remain): http://monarchwatch.org/chip

- Create a Monarch Waystation habitat: http://monarchwatch.org/waystations

- Join the Bring Back the Monarchs campaign: http://bringbackthemonarchs.org

---------------------------------------
About This Monarch Watch List
----------------------------------------

Monarch Watch (http://monarchwatch.org) is a nonprofit educational
outreach program based at the University of Kansas that focuses on
the monarch butterfly, its habitat, and its spectacular fall
migration.

We rely on private contributions to support the program and we need
your help! Please consider making a tax-deductible donation. Complete
details are available at http://monarchwatch.org/donate or you can
simply call 800-444-4201 (KU Endowment Association) for more
information about giving to Monarch Watch.

If you have any questions about this email or any of our programs
please feel free to contact us anytime.

Thank you for your continued interest and support!

Monarch Watch
http://monarchwatch.org
monarch@ku.edu

You are receiving this mail because you subscribed to the Monarch
Watch list via monarchwatch.org or shop.monarchwatch.org - if you
would rather not receive these periodic email updates from Monarch
Watch please visit http://monarchwatch.org/update/

This e-mail may be reproduced, printed, or otherwise redistributed as
long as it is provided in full and without any modification. Requests
to do otherwise must be approved in writing by Monarch Watch.

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