How do you count monarch butterflies?

       Every year thousands of butterflies spend their winters on the California Central Coast. The monarchs have just begun to arrive in Pacific Grove, and our first count of the season was conducted earlier this week. There are currently 200 monarch butterflies in the Pacific Grove Monarch Sanctuary. More and more monarchs will continue to arrive each day until the population peaks around Thanksgiving. Last year our count at the peak of the population was over 13,000 monarchs.  One question both staff and volunteers are often asked is, How do you count them all? It seems like an almost impossible task, however, hundreds of people throughout California, spend time counting these butterflies at their different wintering sites every year.

      If we were to capture and count every single monarch butterfly, it would take all day, and we would be disturbing the butterflies and their habitat. Instead, we use estimation. To count the monarchs, we follow the counting protocols that were not only taught to our organization, but to anyone who wishes to help count the monarchs at any of the wintering sites from San Francisco to San Diego. The Xerces Society, an organization that promotes the protection and conservation of invertebrates, and California Polytechnic State University’s Monarch Alert program are two organizations that help train California volunteers.

        So, how do we count? We look at the monarchs in small clusters. A cluster is a group of 3 or more monarchs that are close together. A cluster can be large, and it can be difficult to see the individual butterflies within a cluster without the help of binoculars or a scope. Clusters can range in size from 30, to a few hundred or even a thousand monarchs. We do not count every monarch in a cluster, as this would take too much time and lead to fatigue of the counter. Instead, we count a small section of that cluster and use it to estimate how many total monarchs are in a particular cluster.

Monarch Cluster

      For example, if we were to count the cluster pictured above, here’s how we would go about it. It’s rather large, so we would count an area of 10 monarchs – which we’ve gone ahead and highlighted in red below.

Monarch cluster count of 10

           After we’ve counted 10 individual monarchs, we look at how big of an area 10 monarchs takes up in that cluster.

Monarch Cluster group of 10

         Then we estimate how many times that group of 10 would fit throughout the rest of the cluster.

Monarch Cluster 30 groups of 10

           For this cluster we estimated that our original group of 10 fits in this cluster a total of 30 times, which means we estimate there to be 300 monarchs in this particular cluster. Wow. That’s a lot of monarchs in one small area. We would then go and count the rest of the clusters found in the Sanctuary.

            The largest cluster we had to count at the Sanctuary last year was one that took up an entire branch of a pine tree and have over 4,000 monarch butterflies.

            As you can imagine, it still takes a while to count the monarchs this way. When you stop by the Sanctuary later in the seaon, you’ll see there are lots of monarch clusters to count. Also, if you’ve been there on a warm afternoon, you’ve seen the monarchs flying around everywhere. There’s no way we can count the monarchs if they’re flying around, so counters have to get up early, and arrive at the Sanctuary at sunrise, when the monarchs are still too cold to move. If the counters aren’t properly equipped with enough coffee, sometimes they can be just as immobile as the monarchs they're there to observe.

        It’s a lot of work, but it’s really rewarding to get to spend the early morning hours with the monarchs.