Mourtisen, Henrik5; Derbyshirec, Rachael8; Stalleickena, Julia5; Mouritsen, Ole Ø.1; Froste, Barrie J.7; Norrisc, D. Ryan8
1 Computer Aided Engineering Design and Product Development, The Faculty of Engineering and Science (ENG), Aalborg University, VBN2 Solid and Computational Mechanics, The Faculty of Engineering and Science, Aalborg University, VBN3 Department of Mechanical and Manufacturing Engineering, The Faculty of Engineering and Science, Aalborg University, VBN4 The Faculty of Engineering and Science (ENG), Aalborg University, VBN5 Research Centre for Neurosensory Sciences, University of Oldenburg, 26111 Oldenburg, Germany6 University of Guelph7 Department of Psychology, Queen’s University, Kingston, ON, Canada K7L 3N68 University of Guelph
Monarch butterflies (Danaus plexippus) breeding in eastern North America are famous for their annual fall migration to their overwintering grounds in Mexico. However, the mechanisms they use to successfully reach these sites remain poorly understood. Here, we test whether monarchs are true navigators who can determine their location relative to their final destination using both a “compass” and a “map”. Using flight simulators, we recorded the orientation of wild-caught monarchs in southwestern Ontario and found that individuals generally flew in a southwest direction toward the wintering grounds. When displaced 2,500 km to the west, the same individuals continued to fly in a general southwest direction, suggesting that monarchs use a simple vector-navigation strategy (i.e., use a specific compass bearing without compensating for displacement). Using over 5 decades of field data, we also show that the directional concentration and the angular SD of recoveries from tagged monarchs largely conformed to two mathematical models describing the directional distribution of migrants expected under a vector-navigation strategy. A third analysis of tagged recoveries shows that the increasing directionality of migration from north to south is largely because of the presence of geographic barriers that guide individuals toward overwintering sites. Our work suggests that monarchs breeding in eastern North America likely combine simple orientation mechanisms with geographic features that funnel them toward Mexican overwintering sites, a remarkable achievement considering that these butterflies weigh less than a gram and travel thousands of kilometers to a site they have never seen.
Proceedings of the National Academy of Science of the United States of America, 2013, Vol 110, Issue 18