Are Monarch Butterflies Losing Their Migration Instinct?
Beginning in June 2006, butterfly gardens with milkweed plants (Asclepias) in the Southwest have had more monarchs flying in their gardens than any previous year since the Monarch Program was founded in 1990. There have been numerous requests for milkweed plants from people with defoliated plants due to monarch larvae consuming the leaves. This demand has often resulted in sold-out situations with nurseries throughout the Southwest during the summer and autumn months since 2006.
Several tagging experiments have recently been conducted in order to monitor autumn migrants that emerged as adults from wild monarch livestock. In 2006, 112 locally reared monarchs were tagged and released from October 4th through November 16th, within 12-20 miles east of the San Diego coast/bay. Some were reported within days of their release and one was retrieved dead (5 miles east of its release point) at an elementary school butterfly garden several weeks after its release. No tagged monarchs were sighted during a visit to 17 monarch overwintering sites from San Diego to Santa Barbara Counties by Monarch Program volunteers in November and December of 2006.
In the autumn of 2007 in San Diego County, 55 reared monarchs from La Mesa were tagged and released from November 2nd through the 17th. In Escondido, 45 reared and tagged monarchs were released from October 28th through November 10th. None of the monarchs were sighted at overwintering sites visited by Monarch Program volunteers between November 16th and December 9th at 33 sites from San Diego to Santa Barbara Counties.
Monarchs in the Southwest seem to be “happy” during the winter days living in people’s backyards as opposed to diapausing a few months near the coast on eucalyptus trees. The number of monarchs reported locally in backyard gardens during the winter months is unusual. They are behaving as a butterfly that has no reason to migrate to the coast. They have host plants, shrub/tree protection in most areas, nectar sources, and warm weather.
Monarch butterflies along the coast of Santa Barbara have occupied people’s backyards every month of the year since records were kept since the 1960’s. Some resident monarchs fly a few miles to live with other monarchs at nearby overwintering sites. They migrate a mile or two to overwintering sites and hang-out for a few months. Santa Barbara has more monarch overwintering sites, including year-round resident monarchs, than any other county in California.