(IMAGE) University of Ottawa Caption The averaged assignment maps for the 100 monarchs. Darker shades indicate areas where the butterflies are more likely to have originated. The black dots mark the sites that monarchs were collected from in Spring 2011 during their northward migration from the overwintering sites in Mexico to their summer breeding grounds in the USA and Canada. Dual strontium-hydrogen assignment (green) resulted in the smallest area of estimated natal origin compared to hydrogen (blue) and strontium (red). It is interesting that most of the monarchs in our sample originated in Texas, as most overwintering monarchs are thought to come from the Midwest. More research is needed to confirm this result. Credit Megan Reich, University of Ottawa Usage Restrictions None License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.