COSEWIC Assessment and Status Report on the Monarch Danaus plexippus in Canada SPECIAL CONCERN 2010 COSEWIC status reports are working documents used in assigning the status of wildlife species suspected of being at risk. This report may be cited as follows: COSEWIC. 2010. COSEWIC assessment and status report on the Monarch Danaus plexippus in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vii + 43 pp. (www.sararegistry.gc.ca/status/status_e.cfm). Previous report(s): COSEWIC. 2001. COSEWIC assessment and update status report on the Monarch Danaus plexippus in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. v + 21 pp. (www.sararegistry.gc.ca/status/status_e.cfm). 1997. Draft. COSEWIC status report on the Monarch Danaus plexippus in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. Production note: COSEWIC would like to acknowledge Karine Bériault for writing the status report on the Monarch (Danaus plexippus) in Canada, prepared under contract with Environment Canada. This report was overseen and edited by Laurence Packer, Co-chair of the COSEWIC Arthropods Species Specialist Subcommittee. For additional copies contact: COSEWIC Secretariat c/o Canadian Wildlife Service Environment Canada Ottawa, ON K1A 0H3 Tel.: 819-953-3215 Fax: 819-994-3684 E-mail: COSEWIC/[email protected] http://www.cosewic.gc.ca Également disponible en français sous le titre Ếvaluation et Rapport de situation du COSEPAC sur le monarque (Danaus plexippus) au Canada. Cover illustration/photo: Monarch — Bob Graham, Point Pelee National Park. ©Her Majesty the Queen in Right of Canada, 2010. Catalogue CW69-14/597-2010E-PDF ISBN 978-1-100-15945-4 Recycled paper COSEWIC Assessment Summary Assessment Summary – April 2010 Common name Monarch Scientific name Danaus plexippus Status Special Concern Reason for designation This species has a population of millions to over one billion individuals. The most sensitive stage of its annual cycle is overwintering. There are two main overwintering areas: the Oyamel Fir forests of Central Mexico, where 90% of the population overwinters, and coastal regions of California. The overall area of these sites is relatively small, and threats, especially from logging in the Oyamel Fir forests, are sufficient to suggest that the species could become Threatened in the near future. Occurrence British Columbia, Alberta, Saskatchewan, Manitoba, Ontario, Quebec, New Brunswick, Prince Edward Island, Nova Scotia Status history Designated Special Concern in April 1997. Status re-examined and confirmed in November 2001 and in April 2010. iii COSEWIC Executive Summary Monarch Danaus plexippus Species information The Monarch is a large, showy, orange and black butterfly. The wings, which span 93-105 mm, are mostly orange with a broad black border and two rows of circular white spots. The chrysalis is of a spectacular green and gold. The larva is distinctively white, yellow, and black-banded, with a pair of black filaments at its head and tail. Distribution The Monarch is widely distributed in the New World and is found from Central America northwards to southern Canada, and from the Atlantic Coast westward to the Pacific Coast. Populations have been introduced to numerous other parts of the world. The Monarch has been recorded from all ten provinces and in the Northwest Territories. The northern limit of the breeding range corresponds with the northern range limit of milkweeds at about 54 ˚N in the central prairie provinces. Monarch populations in Canada overwinter in two distinct regions: over 90% of the Canadian population overwinter mostly in the mountains of Central Mexico whereas the southern British Columbia individuals overwinter in coastal California. Habitat The Mexican overwintering sites (for populations referred to below as “eastern”) are in the Oyamel Fir Forests of Central Mexico where millions of adult Monarchs aggregate in a small number of sites. In California, the overwintering habitat is along the coast south to Baja California where ~400 overwintering sites have been recorded. Individuals from these sites are referred to as “western”. The breeding habitat of the Monarch is confined to sites where milkweeds, the sole food of the caterpillars, grow. Different milkweed species grow in a variety of environments and are also planted in gardens. iv Biology The Monarch, like all butterflies, has a life cycle that is composed of four stages: egg, larva (or caterpillar), pupa (or chrysalis), and imago (or adult butterfly). Female Monarchs lay up to 500 eggs on the undersides of milkweed leaves. The caterpillar transforms into a chrysalis, metamorphoses, and emerges later as a butterfly. In most of southern Canada, the late summer adults migrate south to Mexico, where they overwinter. Overwintered adults begin flying north in late February or early March. Females that leave the overwintering sites breed in the coastal states of the Gulf of Mexico and die. Adults of the following generations continue the migration north, although some stay to breed locally. Butterflies from southern British Columbia undergo a shorter migration from the overwintering sites along the coast of California to the breeding range, which includes areas in Arizona and New Mexico north to southern British Columbia. There is exchange of individuals across the Rocky Mountains: Central Mexican and Californian overwintering individuals are not genetically distinct. Population sizes and trends Eastern and Western populations fluctuate frequently, sometimes dramatically, as a result of overwintering mortality, poor breeding conditions, mortality due to pesticides and herbicides, and predation. The Western population likely numbers in the millions. The overwintering Eastern population is estimated to range from 110 million to nearly 1 billion. Since 1993, the combined area of all overwintering colonies in Mexico measured in any one year ranges from 0.02 to 0.181 km2. Large numbers of Monarchs breed in Canada each year and the breeding range varies from year to year depending on weather conditions and the abundance of the larval plant host. Limiting factors and threats Forest degradation at the overwintering sites is likely the biggest threat facing the Monarch. For the Eastern population, the various causes of this include conversion of forest to agriculture and pastures, excessive commercial logging (legal and illegal) and, more recently, tree mortality due to bark beetle damage. Some of the habitat is protected by presidential decree but is still being logged. These logging practices create openings and thinned areas in the forest, which increase the exposure of overwintering Monarchs to winter storms, cold temperatures and wet conditions, resulting in increased and sometimes substantial mortality. Modelling of future climate scenarios suggests that climate change will reduce the area of suitable forest at the overwintering sites in Mexico. Increased frequency of cool, wet summers reduces the Monarch population growth rates. For the Western population, habitat degradation is caused mainly by real estate development along the California coast and by elimination of introduced eucalyptus upon which the butterflies overwinter. v Herbicide and pesticide use across North America is a threat. Milkweeds are still listed under the Noxious Weed acts of Manitoba, Ontario, Quebec and Nova Scotia. Special significance of the species The migration that is undertaken by the Eastern population is unique, is currently facing numerous obstacles, and has been described as an endangered biological phenomenon. The Monarch is an international symbol of nature; cooperation among Canada, Mexico and the USA as part of the free trade agreement; and is used in classrooms all over North America to teach children about life, biology, metamorphosis, conservation, and an appreciation for nature. Existing protection The Monarch was designated as Special Concern by COSEWIC in 1997. The status was re-examined and confirmed in 2001. In Ontario, Monarchs receive protection under the Fish and Wildlife Conservation Act. vi COSEWIC HISTORY The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list. On June 5, 2003, the Species at Risk Act (SARA) was proclaimed. SARA establishes COSEWIC as an advisory body ensuring that species will continue to be assessed under a rigorous and independent scientific process. COSEWIC MANDATE The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assesses the national status of wild species, subspecies, varieties, or other designatable units that are considered to be at risk in Canada. Designations are made on native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fishes, arthropods, molluscs, vascular plants, mosses, and lichens. COSEWIC MEMBERSHIP COSEWIC comprises members from each provincial and territorial government wildlife agency, four federal entities (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biodiversity Information Partnership, chaired by the Canadian Museum of Nature),