Monarch Monitoring

You don’t have to be a monarch expert or a trained scientist to count monarch butterflies. You do, however, need to be willing to wake up early and stare high into the trees for long periods of time. Did we mention that it’s cold? Well, it’s cold. It’s cold and it’s early, but it is also amazing.

Each year, thousands of monarch butterflies (Danaus plexippus) migrate to Pacific Grove and other overwintering sites along the California coast. Not one of the traveling butterflies has made the journey before, yet many thousands manage to find special groves of trees offering the conditions required of a sufficient winter home. Needless to say, the spectacle of the monarch butterfly’s fall arrival, overwintering, and eventual spring mating and dispersal, is nothing short of breathtaking.

Community scientists with the Pacific Grove Museum of Natural History have been counting monarch butterflies for more than 5 overwintering seasons, and we’ve confirmed that there’s no way to avoid those cold and early mornings. This is due to the monarch butterfly’s ectothermic (cold-blooded) nature, and the fact that they cannot fly if it is colder than approximately 55°F. Since 1000’s of monarchs in-flight would be impossible to count, a typical monarch survey begins around sunrise, when temperatures are still low.

Equipped with binoculars, data-sheets, and weather meters, community scientists begin each count with a walk through the site and a recording of important environmental parameters. The data sheet calls for the temperature, wind speed, cloud cover, and precipitation, and each is dutifully recorded as baseline information. These data points, along with the eventual number of monarchs, will help paint a long-term picture of how monarchs move within a site under differing conditions. For instance, do monarchs show a tree species preference when wind speeds pick up? Do they cluster lower to the ground when it is raining? Are monarchs more densely clustered when it is cloudy? These are just a few of the questions that may be answered by years of cold, early morning counts.

Once weather data are recorded the count can begin. Using binoculars and a Xerces-approved counting protocol, small teams of community scientists count cluster by cluster, attempting to locate and account for every monarch butterfly at the site. A meticulous method of estimation and extrapolation helps to make quick work of the seemingly daunting task of counting thousands (sometimes tens of thousands) of monarchs. A typical survey of a medium-sized site will take between 1 - 1.5 hours, and will result in the total number of monarch butterflies at that site on that day. This number is added to a Museum database, and is also submitted to the Xerces Society for Invertebrate Conservation, where it will help inform scientific reports, conservation, and policy-making.

This school year, the Museum’s education team is getting local middle and high school students involved in monarch community science. After an in-class training session and a practice count at the PG Monarch Sanctuary, local students will begin collecting important monarch count data. They will also learn what it means to do science, and will discover the important role that science will play in our communities of the future.