Early data from Western Monarch Thanksgiving Count suggests a small increase in butterfly numbers in some parts of the overwintering range
By Xerces Society on 14 Dec, 2015
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Populations of monarch butterflies are still far below historic numbers
PORTLAND, Ore., December 14, 2015 — First reports from monarch overwintering sites in California surveyed during the Xerces Society’s Western Monarch Thanksgiving Count suggest that 2015 may have been a better year for the beleaguered monarch butterfly in the western United States. The overall population size is still far lower than it was in the 1990s, when more than one million butterflies were counted.
The surveys indicate that sites north of Santa Cruz are hosting more butterflies than previous years, whereas sites in Monterey, San Luis Obispo, and Santa Barbara Counties are reporting fewer numbers of butterflies on average. Several new sites have been reported, including some from Marin County with up to 10,000 monarchs. The data is not yet available for Santa Cruz County and southern California.
“The count data that our volunteers are now sending in give a first glimpse at the number of monarchs overwintering in California,” said Sarina Jepsen, director of the Xerces Society’s endangered species program. “We’re happy that numbers seem to be higher at some of the northern California sites that have been surveyed, but monarch populations have not yet recovered in the western U.S.”
Monarchs from as far away as Idaho and Arizona converge on tree groves along the California coast to spend the winter. Because most monarchs from the western United States are clustered together on the coast, an accurate assessment of the health of western monarch populations is possible.
The Xerces Society’s Western Monarch Thanksgiving Count began in 1997 and is the longest running effort to monitor overwintering monarchs in California. The count happens during a three-week period centered on Thanksgiving. Biologists, land managers, and citizen scientists visit overwintering sites year after year to monitor the butterflies. This year, more than 85 volunteers surveyed over 130 sites. A complete analysis of the 2015 Western Monarch Thanksgiving Count will be available in late January 2016.
“It is exciting to begin to get a picture of how many butterflies are arriving to spend the winter,” said Candace Fallon, count coordinator for the Xerces Society. “Volunteer efforts such as this are critically important to understanding the status of western monarch butterflies.”
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