Newsroom Midwest Region

New technology for counting wintering monarchs

January 3, 2018

Clusters of overwintering butterflies in California. Photo by Lisa Hupp/USFWS.
Clusters of overwintering butterflies in California. Photo by Lisa Hupp/USFWS.

North American monarch butterflies undertake an annual migration phenomenon that results in densely clustered overwintering colonies at sites in California and Mexico. Numbers of overwintering monarchs can reach up to tens of thousands of monarchs per site in California to tens of millions of monarchs per site in Mexico. Overwintering population estimates are the primary means for monitoring the North American monarch population—information that is increasingly important given long-term population declines observed since monitoring began in the early 1990s. With thousands or millions of monarchs clustered on a few trees, precise estimates of their population can be difficult.

Light Detection and Ranging, known as LiDAR remote sensing technology is commonly used to map topography at broad scales. However, this high-resolution mapping technique has been used to map archaeological sites and cave structures, and recently has proven promising for assessing gray bat populations, a species that exhibits dense-clustering patterns comparable to monarchs. By mapping surface area with monarchs present, and again once monarchs have dispersed, it may be possible to produce precise estimates of abundance of overwintering colonies. If successful, this technique can be employed with partners in Mexico to provide more accurate population estimates and may also prove a useful tool for documenting the larger colonies in California.

Back in December 2016, in collaboration with Winston-Salem State University’s Center for Design Innovation and the U.S. Geological Survey, we piloted ground-based LiDAR technology on colonies of monarchs overwintering along the central coast of California. The effort was supported by the Xerces Society, whose members conduct manual counts each year. Information was collected from three sites in California - Pacific Grove, Lighthouse Field and Pismo Beach.

Building upon the information collected, we recently launched a two-year project with the Center for Design Innovation to further develop appropriate methods, analysis techniques and testing. In addition to LiDAR, we will be incorporating thermal imagery, high-resolution videography, and other technologies to count and map the overwintering monarchs and their habitat. This project will ultimately help us more accurately count how many monarchs are overwintering each year -  one of five priority research topics identified by the Trinational Monarch Conservation Science Partnership.

Along with the science, a second application of communication tools and education materials will be designed to increase public engagement and potential for virtual access to overwintering grounds. This radical collaborative design of bringing together engineers, architects, scientists and communicators is novel to capture the structure of monarch overwintering habitat and allows to see more than a human’s eye when counting.