Annual Count Shows that Number of Monarch Butterflies Overwintering in California may be Holding Steady

For Immediate Release

January 14, 2015

Contact: Scott Hoffman Black, Executive Director, Xerces Society; (503) 449-3792,

Annual Count Shows that Number of Monarch Butterflies Overwintering in California may be Holding Steady

Data released today show that monarch butterfly populations at overwintering sites in California may be remaining stable. Volunteers with the 2014 Xerces Society Western Monarch Thanksgiving Count visited 185 sites, nearly two dozen more than the previous year, and tallied a total of 234,731 monarchs. This is up from the 211,275 counted in 2013. However, the average number of butterflies per site was slightly down, and the overall increase is likely due to the fact that more sites were surveyed this fall.

Now in its 18th year, the Western Monarch Thanksgiving Count spans three weeks over the Thanksgiving holiday and is supported by over 150 volunteers throughout the state. Data collected over the 18 years show a considerable decline in the number of overwintering monarchs. In 1997, the first year of the count, over 1.2 million monarchs were recorded at 101 sites (an average of 12,232 monarchs per site). In 2014, just 234,731 monarchs were counted at 185 sites—an average of only 1,268 monarchs per site, representing a decline of 81 percent from the 1997 high and a 48 percent decline from the 18-year average.

Monarch butterflies spend the winter in spectacular accumulations in a small number of sites in the oyamel fir forests of central Mexico and at hundreds of forested sites scattered along a 620 mile stretch of the Pacific coastline from Mendocino County, California, to Baja California, Mexico. Each year, citizen scientists with the Western Monarch Thanksgiving Count visit California overwintering sites to estimate monarch populations. Volunteer efforts such as this are critically important to understanding the status of western monarch butterflies.

Estimating the numbers of overwintering butterflies is the best way to gauge the status of the monarch population. Scientists believe loss and degradation of both breeding and overwintering habitat, pesticide use, and drought—exacerbated by climate change—may all be contributing to the decline in monarch numbers.

Citation for graph data:
Monroe, M., C. Fallon, D. Frey, and S. Stevens. 2015. Western Monarch Thanksgiving Count Data from 1997–2014. Available at:


The Xerces Society for Invertebrate Conservation
Protecting the Life that Sustains Us
The Xerces Society is a nonprofit organization that protects wildlife through the conservation of invertebrates and their habitat. Established in 1971, the Society is at the forefront of invertebrate protection worldwide, harnessing the knowledge of scientists and the enthusiasm of citizens to implement conservation programs.