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northern Indiana, Illinois, Iowa, Michigan, or the upper Midwest compared to the 1996 breeding
season.
Flockhart et al. (2013) went beyond study of the overwintering generation to determine the natal
origins of successive monarch generations produced in the east throughout the 2011 breeding
season. The natal origins showed a broad spatial distribution that encompassed the entire
breeding range in eastern North America, though the preponderance of individuals originated
from northern Texas to western Ohio, in a region extending from the southern Great Plains
through the Midwestern Corn Belt (Figure 16). Over this particular breeding season, fewer
butterflies originated in the upper Midwest, northeastern and eastern states, and southern Canada,
than in the Texas-to-Ohio zone. There were few indications of natal origins from Mississippi,
Alabama, Georgia and Florida despite the fact that areas located north of these locations were
sampled extensively.
Figure 16. Probability distribution for natal origins of monarchs collected in eastern North
America during the 2011 breeding season, based on isotope analysis of butterflies. Red dots
represent monarch capture locations. The color gradient on the map (light green to dark blue)
represents the natal origins of the 839 butterflies analyzed, with increasing numbers of butterflies
born in areas with progressively darker coloration, as indicated by the scaled bar to the right of
the map. Figure 3 from Flockhart et al. (2013), original caption omitted.
Monarch ESA Petition 42