[Leps-l] Monarch decline - data and publications

[Chip Taylor]

For those of you interested in data, here are 
some links to data and publications that pertain 
to the decline in monarch numbers. It is likely 
that the overwintering numbers for 2012-2013 will 
be the lowest recorded to date.


Record of fall roosts - allows you to compare 
years and dates - and those can be compared to 
overwintering numbers - see below

http://www.learner.org/jnorth/tm/monarch/MigrationMapsFallRoost.html

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Spring migration - allows you to compare years and dates

http://www.learner.org/jnorth/tm/monarch/MigrationMaps.

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Size of overwintering populations -- measured by 
personnel from WWFMX and the MBBR.

http://www.learner.org/jnorth/tm/monarch/PopulationMexicoAnalyzeGraph.html


See also - 
http://monarchwatch.org/bring-back-the-monarchs/campaign/the-details 
- for some data on Western monarchs



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Milkweed loss in agricultural fields because of 
herbicide use: effect on the monarch butterfly 
population
	.	JOHN M. PLEASANTS1, KAREN S. OBERHAUSER
Issue

Insect Conservation and Diversity - March 2012

Keywords:
		Glyphosate;GMO;milkweed;monarch butterfly
Abstract. 1.?The size of the Mexican 
overwintering population of monarch butterflies 
has decreased over the last decade. Approximately 
half of these butterflies come from the U.S. 
Midwest where larvae feed on common milkweed. 
There has been a large decline in milkweed in 
agricultural fields in the Midwest over the last 
decade. This loss is coincident with the 
increased use of glyphosate herbicide in 
conjunction with increased planting of 
genetically modified (GM) glyphosate-tolerant 
corn (maize) and soybeans (soya).
2.?We investigate whether the decline in the size 
of the overwintering population can be attributed 
to a decline in monarch production owing to a 
loss of milkweeds in agricultural fields in the 
Midwest. We estimate Midwest annual monarch 
production using data on the number of monarch 
eggs per milkweed plant for milkweeds in 
different habitats, the density of milkweeds in 
different habitats, and the area occupied by 
those habitats on the landscape.
3.?We estimate that there has been a 58% decline 
in milkweeds on the Midwest landscape and an 81% 
decline in monarch production in the Midwest from 
1999 to 2010. Monarch production in the Midwest 
each year was positively correlated with the size 
of the subsequent overwintering population in 
Mexico. Taken together, these results strongly 
suggest that a loss of agricultural milkweeds is 
a major contributor to the decline in the monarch 
population.
4.?The smaller monarch population size that has 
become the norm will make the species more 
vulnerable to other conservation threats.
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Decline of monarch butterflies overwintering in 
Mexico: is the migratory phenomenon at risk?
	.	LINCOLN P. BROWER1, ORLEY R. 
TAYLOR2, ERNEST H. WILLIAMS3, DANIEL A. 
SLAYBACK4, RAUL R. ZUBIETA5, M. ISABEL RAMÍREZ6

  Insect Conservation and Diversity
Volume 5, Issue 2, pages 95-100, March 2012

For the abstract visit -- 
http://onlinelibrary.wiley.com/doi/10.1111/j.1752-4598.2011.00142.x/abstract


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Brower, L.P., O.R. Taylor, & E.H. Williams. 2012. 
Response to Davis: choosing relevant evidence to 
assess monarch population trends. Insect 
Conservation and Diversity, in press. (published 
on-line October, 2011; doi: 
10.1111/j.1752-4598.2011.00176.x)

For the abstract visit --- 
http://onlinelibrary.wiley.com/doi/10.1111/j.1752-4598.2011.00176.x/abstract