Monarch Cluster

The Monarch Dunes Butterfly Habitat was once part of a 957 acre Tasmanian blue gum eucalyptus plantation in Nipomo, California, and has supported as many as 60,000 overwintering monarch butterflies.  As part of the mitigation of the development of this parcel of land for homes, golf courses and a hotel resort complex, nineteen acres surrounding the historic aggregation area were identified as critical for its integrity and, in 2006, were preserved as a sanctuary for overwintering monarch butterflies, now known as the Monarch Dunes Butterfly Habitat.

In addition to securing the sanctuary, an endowment was established to manage the protected grove as a permanent overwintering site for the butterflies.  The management of monarch butterfly winter sites is key to the preservation of their mass winter aggregations in California.  Environmental studies have shown that monarch butterflies are attracted to the microclimatic conditions created by a grove and surrounding vegetation and topography rather than to any particular tree species.  Management of winter sites in California is becoming more critical because many of these sites are limited to discrete forested areas.  These forested areas are living entities that are susceptible to natural forces such as diseases, insects, storm damages and grove senescence.

Management involves the monitoring of the conditions for winter aggregations and, when necessary, restoring these conditions through purposeful grove modification and enhancement activities.  The development of Trilogy at Monarch Dunes involved the removal of trees surrounding the sanctuary and removal of debris, excess litter and fallen trees within the habitat for public safety.  These activities had a major negative effect on the conditions for winter aggregations.  The grove’s wind profile showed that winds (≥2 meters/second or 4.5 miles/hour), disruptive for roosting butterflies, flowed freely through the grove, especially in areas that had or once supported winter aggregations.  Only 50 butterflies were observed during the 2005-2006 season, and they were absent by late November when these winds invaded the cluster arena.

Consequently, strategic plantings of Monterey cypress trees along the western border of the sanctuary were done to reduce the velocity of future disruptive winds from the northwest.  Five additional cypress trees were planted within the sunlit cluster arena to provide future wind-sheltered foliage for roosting butterflies.

Kingston Leong
Dr. Kingston Leong

In 2010, the Monarch Dunes Butterfly Habitat Volunteer Committee (MBHVC) was formed to continue the environmental monitoring, data analyses and management of Monarch Dunes Butterfly Grove.  This committee works with San Luis Obispo County, the Woodlands Master Association, and Dr. Kingston Leong, monarch habitat consultant, Professor Emeritus, California State University, to manage the grove conditions for the overwintering monarch butterflies.  The committee also developed a software program currently in use to analyze the environmental and biological data and to make management decisions.

Grove conditions are slowly recovering and stabilizing for winter aggregations.  In 2010-2011 there were 1,500 butterflies.  In 2011-2012 the numbers increased to 10,000 butterflies.  The grove conditions for both winter seasons were of a transitional site since the butterflies left the grove by January.  This past winter season (2012-2013) had only 5,000 butterflies but, more importantly, the butterflies remained at the sanctuary until the end of the season, indicating that grove conditions are recovering to one of a climax winter site.

Last updated 24 May 2013.