Status, Distribution & Conservation

The Monarch Butterfly, Danaus plexippus L., in Canada


Habitat Requirements, continued...

Abiotic Factors

A number of abiotic (i.e. not biological in origin) factors also delineate suitable habitat. Obvious factors include climate (temperature and humidity) and weather (winds, storms, etc.). Less obvious factors include the use of hostplants that are isolated or occur in standing water and the total amount of sunshine received. For example, larvae spend as much as 90% of the time in which they're not eating "basking" on Milkweed leaves, in full view of potential predators due to their protective colouration, and are able to raise their body temperatures from 3° to 8° C above the ambient air temperature thus shortening their larval period, time in which they are vulnerable to other mortality sources (Dempster 1984), by as much as 50% (Rawlins & Lederhouse, 1981). Associated with the availability of abundant nectar sources is a migratory "window of opportunity" which involves factors such as photoperiod, temperature (cool nights and mild days) and the ability to maintain low temperatures to conserve vital lipid resources (Masters et al. 1988; Gibo & McCurdy, 1993a).

Migratory Staging Areas

The availability of suitable trees for overnight roosts in staging areas is often suggested to be an important factor in staging area site selection, however, Urquhart & Urquhart (1979a) could not substantiate this popular misconception. What does appear to be important is the combination of high quality, abundant nectar sources, abiotic conditions and location. The most popular staging areas, for the Monarchs, appear to be archipelagos or spits of land which provide protection from the elements and the shortest possible distance across large barriers such as the Great Lakes (Brenner 1993; Walton 1993; Wormington 1995; D. Davis, pers. comm.).