Status, Distribution & Conservation

The Monarch Butterfly, Danaus plexippus L., in Canada

General Biology



Monarchs exhibit a number of adaptations for their migration including increased cold-hardiness (Anderson & Brower 1993), reproductive dormancy or diapause (Herman 1981; Urquhart 1987), the ability to actively orient flight direction despite opposing winds and utilize gliding for long distances in order to conserve energy resources (Gibo 1986; Schmidt-Koenig 1993), the ability to store nutrients acquired from nectar sources in the form of lipids which allow for long storage and rapid metabolization of energy reserves (Urquhart 1987; Gibo & McCurdy, 1993a), the ability to behaviourally modify their body temperature to increase flight time (Masters 1993) and maintain lipid mass (Masters et al. 1988), and the ability to maintain their centre of gravity for flight by taking on water to compensate for lipid losses (Gibo & McCurdy, 1993b). Reproductive dormancy, large lipid reserves and the cool temperatures of the overwintering sites interact to greatly increase the lifespan of the migrating brood.

Spring migration into Canada depends greatly on the weather conditions experienced in any particular year but generally butterflies arrive in late May/early June in southern Ontario and in mid-June to early July throughout the rest of the country. Fall migration from southern Ontario is very well documented (Urquhart 1987; Walton 1993; Brenner 1993; Wormington 1994; D. Davis, pers comm.) by the tagging programs which eventually enabled the discovery of the Mexican overwintering sites (Urquhart 1987). Numbers can be very high (Wormington, 1994, estimates that as many as 96,000 butterflies moved through Point Pelee National Park in the space of a few hours on September 6, 1993) but more typically range from 100 - 500 butterflies per day (Brenner 1993; D. Davis, pers. comm.). Data on migration through other provinces is scarce.