You, like I, have probably taken for granted the monarchs overwintering in Mexico are borne in the the northern states of the eastern migration route, since the Midwest seems to be the most predominant migration route. However, by analyzing stable isotopes* from the bodies of over-wintering monarchs and comparing them to known geographic variation, researchers have recently confirmed the birthplaces of eastern monarchs are spread all along the northern regions of the USA and southern Canada, as well as east of the Rocky Mountains.
Not quite so evident was the percentage of monarchs coming from the various regions. It seems that weather’s temperature and precipitation affected the proportions of monarchs originating in the various regions from year to year. But those originating in the Midwestern region always provided the largest percentage.
So what does this tell us? That in order to help maintain our beloved monarch butterflies, it will be necessary to provide appropriate habitat for them throughout America and Canada, and not just in the Midwest. So don’t hesitate. Right now is the time to start planning to increase your milkweed production and add more pollinator plants to your landscape.
*Stable isotopes are similar to chemical fingerprints.
To buy milkweed plants, go Monarch Watch.
To find out more about monarchs conservation, go to Monarch Joint Venture.
To find out more about establishing an appropriate habitat, go to Getting Started with Natural Landscaping