Monitoring Monarch Sites
Annual Thanksgiving Monarch Butterfly Count
A monitoring project called the Thanksgiving Monarch Butterfly Count was started by members of the Monarch Program in 1997. It is similar to the Audubon Society’s Christmas Bird Count and the North American Butterfly Association’s Fourth of July Butterfly Count. These two organizations count the number of different species, whereas the “monarch people” only count the total number of one species at numerous overwintering sites. These numbers are estimates of how many butterflies are in aggregations, perching individually on foliage, and/or flying. Weather conditions, preferred roosting trees, numbers mating, peculiar behaviors, tagging data, and location of aggregations are recorded for annual and long term comparisons.
The choice of a Count in late November is because most monarchs in the west arrive along the coast at selected groves of trees during this time. The Count period is basically from 15 November through 10 December. Climate changes usually occur before the winter solstice and this change influences monarchs to shift to more protected habitats. Thus, a study of population numbers in January or February will be different from those of late November.
Numbers of monarchs estimated at overwintering sites since 1997 can be found in the “Thanksgiving Count” archive. The numbers reflect observations from trained volunteers. Not all sites can be checked every season. However we now have baseline data for population fluctuations. When sites were not visited, no number appears in the space on the chart.
Recommendations for Estimating Overwintering Monarch Butterfly Populations
By David F. Marriott, Ph.D.
Director, Founder (1990)
The Monarch Program
Recording monarch populations at overwintering sites in California gives us valuable information about annual population fluctuations. We can also asses the influence of climate conditions before and during their migration from year to year. Monarchs are basically settled into their chosen sites beginning in mid November, thus the name Monarch Thanksgiving Count. The name was inspired by The Audubon Society Christmas Bird Count.
Do not use an exact number for a population estimate, such as 2,761. It’s an estimate. Round the numbers off so it would be 2,700 or 2,800, or maybe 2,750. When there are less than fifty monarchs at a site, each one should be counted. Otherwise, there is no need to include single numbers, especially when there are more than 2,000 monarchs.
Tips for Estimating
Use of Binoculars: Estimates can be more accurate when using binoculars. They are essential when visiting sites. Binoculars enable us to see butterflies behind others which we would not see with the naked eye, or others would look like leaves. I use 10X26 power, field 520, 273 ft./1000 yrds. For long distances when I don’t have close access to the roosting trees, I use 22X100 power, field 2.80, on a tripod.
Locating Roosting Trees at Overwintering Habitats: Some people visit overwintering sites and cannot find the monarchs, especially on cool days when they are not flying and appear camouflaged in the leaves. When we are near the Winter Solstice, monarchs often begin to shift to other trees or even different sites. I suggest people request a satellite image of where monarchs are usually located in late November by contacting email@example.com. They almost always roost on the southeast side of the trees, in protected areas, to take advantage of the morning through evening sunlight.
Learning to Count: Volunteers need to begin with counting small clusters of monarchs, maybe no more than several in a population of 200. It can be overwhelming when beginners see tens of thousands. First, count 20 monarchs and learn what that number looks like. Start at the bottom of the cluster and count by 20’s moving up the branch. When you learn what a number of 100 look like, then count by 100’s, then by 500’s, 1,000’s, etc. Before visiting sites, first time volunteers should learn estimates by counting monarchs from a photograph. This will help to understand what a certain number looks like before going into the field. When doing counts, you must think about how many are on the backside of the cluster that you cannot see. Information about obtaining photographs is available by e-mailing firstname.lastname@example.org.
Singles and Flyers: When visiting an overwintering site you will see single butterflies basking in the sun on leaves and butterflies flying, especially in the late morning and early afternoon. Single monarchs that are stationary are fairly easy to count. However, counting monarchs that are flying is difficult. You will need to develop a “feel” of about how many monarchs are flying within a certain volume of space and multiply this number with the total number of monarchs counted in each space selected. Most monarchs will be flying near the roosting sites except on very warm sunny days when many will extend their flight area which makes it difficult to obtain a good estimate.
Counting Monarchs on Different Roosting Trees: Monarchs on some trees are very difficult to see or find, especially on pine and cypress trees. Their color and “tight” clusters look very much like clusters of pine nettles. This is also true for Sycamore trees when monarchs match the color of the autumn leaves. The underside of the wings are the same color as the deciduous leaves drying to a light brown-orange color. Volunteers will need to know exactly where monarchs are located in groves with these types of trees.
Feeling Confident about Estimates: When people visit overwinting sites and are asked the question: “How many monarch do you think there are? They would often say thousands, but an experienced counter would say no, there are about 350. Doing counts can be frustrating in the beginning, especially when there are lots of monarchs. With experience it becomes easy and enjoyable because you become a citizen scientist, learn about monarch migration in California, and contribute to a very important data base system. Following the tips should help everyone have a more accurate estimate.