Spring 2001 Red Admiral Migration Observations in North America

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Details of the 2001 migration are described below the map.

About the Spring 2001 North American Red Admiral Migration

The 2001 spring migration of Red Admirals was very noticeable even to casual observers, and may
have been the largest spring migration since that of 1990. There seem to have been two separate waves of migration originating in different parts of the United States.

The first wave appears to have arisen in the area of central Texas, where conditions over the previous winter had been favorable for a large overwintering population to develop. Red Admirals were first observed moving northward in late March in Lawrence, Kansas. A few weeks later, sustained southerly winds from mid-April to mid-May in the midwestern U.S. may have helped large numbers of butterflies to move more rapidly northward. The first large wave of migrators reached central Iowa around April 22, then arrived at Minneapolis, Minnesota around April 28, and reached northeastern Minnesota northwest of Lake Superior between May 7 and May 13. This wave of migration also brought substantial numbers of Red Admirals into southwestern Ontario and western Pennsylvania beginning around April 24. One of these individuals may have reached Prince Edward Island, Canada, on May 8.

The second wave arose in mid-May, probably from somewhere in the southeastern United States. Although its point of origin is less clear, the mid-May observations in northern Georgia, western North Carolina, and near the coast of South Carolina had been the first Red Admirals seen in those locations that spring. In late May, substantial numbers of Red Admirals migrated northward through Virginia, Maryland, New Jersey, Rhode Island, New York, and Pennsylvania. This wave also reached southwestern Ontario. There, a second wave of arrivals came in after the first wave had ebbed. In central Iowa, judging from a change in the mean flight direction, a relatively small number of butterflies from the second wave apparently arrived in late May and continued passing through into early June. Whereas the predominant flight direction through central Iowa during the first wave had been due north, the mean flight heading changed to northwestward on several days during late May. Northwesterly migration was likewise observed in early June in Lawrence, Kansas.

Most data for this map were collected from observers reporting Red Admiral sightings on the Leps-L newsgroup in response to my request for sightings. Some observations were sent directly to me, whereas others were posted on the newsgroup. My thanks to all who made it possible to put this map together.