Status, Distribution & Conservation

The Monarch Butterfly, Danaus plexippus L., in Canada


Historically, there has been no formal protection for the Monarch, or indeed for many insects in general, in Canada. Ontario is the only province that has had butterflies listed as endangered species (since 1976) but no other province has, and no federal laws exist to protect butterflies or other insects. The conservation of insects, butterflies specifically, is a relatively recent concept (Wells et al. 1983; Thomas 1984; New 1991). Pressure to recognize insects as endangered species which are intrinsically worthy of our protection, and butterflies as bio-indicators of general habitat health, is increasing rapidly. The current status of the Monarch in Ontario has been given as "apparently secure with many occurrences" by Holmes et al. (1991). The Natural Heritage Information Centre in Ontario suggests that the status is globally very common, but ranging from extremely rare and very rare, non-breeding to very common, breeding within the province, and continues to track records of the Monarch primarily due to its migratory behaviour (Sutherland 1994). Recently, three areas along the north shore of Lakes Ontario (Prince Edward Point National Wildlife Area) and Erie (Long Point National Wildlife Area and Point Pelee National Park) have been designated as part of an International Network of Monarch Butterfly Reserves (Anon. 1995).

Population Sizes and Trends

Land use changes in Ontario and most southern regions of Canada over the last 200 years have likely served to increase the range of Milkweeds, especially those species such as A. syriaca and A. speciosa which grow in open situations. There is no doubt that Monarch ranges have increased over the last 50 years. Urquhart & Urquhart (1979a) give the breeding range of the Monarch in Ontario during the years 1937-1940 as Kingston to Goderich (approx. 44° N) and south with low numbers breeding in Barrie and Midland to the north. By 1975 they found that the Monarch was commonly breeding along the north shore of Lake Huron from Sudbury to Sault Ste. Marie (47° N) and in Thunder Bay and that in 1977 Monarchs were considerably more common at Sault Ste. Marie than they were at Toronto (Urquhart & Urquhart 1979a). Similarly Urquhart & Urquhart (1979a) reported no breeding in B.C. or Alberta with only scattered larvae recorded through Saskatchewan and Manitoba in the 1940-44 period. More recent records show that breeding does occur in B.C. and Alberta (C. Guppy, pers. comm.; Bird et al. 1995) and that they are now more common in Saskatchewan and Manitoba (Hooper 1973; Klassen et al. 1989). This recent range expansion may slow somewhat but is expected to continue.

The western populations, based on counts at overwintering roosts, have declined over the last five years (Marriott 1994a; 1994b; 1995) possibly due to a Neogregarine protozoan parasite (Leong et al. 1992; Marriott 1993; 1995; Brower et al. 1995). Swengel's (1995) analysis of 4th of July Butterfly Count data shows that both the western and the eastern populations fluctuate dramatically from year to year, often coinciding with major widespread climatic perturbations, but found that no significant increase or decrease in the numbers of Monarchs censused persisted for more than two years. New (1991) and Gaston & McArdle (1993) note that insects whose populations fluctuate dramatically are more likely to become endangered if some catastrophic event occurs at a low point in the natural population cycle. Brower (1995) and others fear that the ongoing degradation and destruction of Mexican overwintering sites may constitute just such a catastrophic event (Wells et al. 1983; Pyle 1983; Brower & Malcolm 1989; Malcolm 1993).