Phenological and isotopic evidence for migration as a life history strategy in Aeshna canadensis (family: Aeshnidae) dragonflies

Abstract

1. Investigating dragonfly migration is important for understanding species' life history strategies, migratory connectivity, terrestrial-aquatic linkages, and for successful species conservation. While migration patterns are well-documented for some species (e.g., Anax junius), questions remain about potential migratory behaviour of others. 2. We investigated the potential for migration of Aeshna canadensis (Walker, 1908; Canada darner) using phenological observations in three study ponds in central Minnesota, 2017–2019. We also conducted probabilistic assignment to natal origins by measuring stable hydrogen isotope values of wing tissue (δ2Hw) of dragonflies collected in Minnesota and acquired through Canadian museum collections. 3. This species emerged May–June from study ponds in central Minnesota, with a 10–15 week lag after onset of emergence before mature adults were observed flying and ovipositing in late summer. The probabilistic assignment depictions of emerging tenerals overlapped with the sampling location, confirming accuracy of isotopic assignments of natal origin. 4. Late-flying mature adults collected at our study ponds likely originated from southern Manitoba, suggesting a north–south migration pathway. We found further evidence for migration by analysing δ2Hw of adult dragonflies collected in northern Minnesota and south-central Canada. Their likely origins were farther north in central Canada (Manitoba/Quebec) or the northeastern reaches of this species' range in eastern Canada. 5. We provide the first conclusive evidence of Aeshna migration in North America and demonstrate a robust approach, combining field observations with probabilistic assignment to origin using stable isotope analysis, which can test for migration in other dragonfly populations.