How Are Monarch Colonies Measured? What Variables Can Affect the Count? It's VERY hard to determine the exact borders of a monarch colony. Imagine how hard it must be for scientists in the field! What do you think could affect their ability to count and estimate the numbers of butterfly trees? THINK first, and then look at this list of variables we came up with. Butterflies Butterflies do not sit motionless in the colonies throughout the winter! Their activity changes throughout the season, from day to day, and even moment to moment. Butterfly activity changes with temperature. The monarchs cluster tightly on trees when they are cold. They can become active and fly around when they are warm. (Suddenly, the trees can look bare!) Butterfly activity changes with sunlight. They often fly around when it's sunny and remain inactive when it's cloudy. Butterfly activity can change after a storm. Storms can force them from their trees to the forest floor. It can take days for them to climb back into the trees. A tree that once had butterflies may no longer appear full enough to count. Butterfly activity can change with moisture needs. (Even in January, they can stream out to drink. What if scientists came then to measure the colony size?) Butterfly activity changes during the season. They are more active as they arrive and depart. Colonies can move unpredictably to a different part of a forest, as this story illustrates. Trees The trees in the forest vary in many ways. Look at pictures of the monarch's forest while you consider these examples. The numbers, arrangement, and length of branches vary. The branches can support different numbers of monarchs. Tree height varies. Some trees are tall, some are short, and some are in between. Spacing of trees varies. Some trees are close together and others are far apart. Trees are three-dimensional, but the measurements are not. Scientists measure only the amount of tree surface the monarchs cover. As these examples show, that can be misleading. Weather Temperatures fluctuate widely from day to day. They're not same each time a scientist visits the colony. (These affect monarch activity.) Storms, wind, rain, sun, clouds affect monarch behavior. Temperatures fluctuate widely in a single day from 30s at night to 70s during the day. When do you think scientists would get the best "butterfly tree" estimates? Why? People Reaching the colonies is difficult. They are remote, hard to reach, and far apart (see map). They form on high mountaintops at elevations at or above 10,000 feet. This can make it hard to measure them over time. It's hard to get up early enough to measure the colonies when the temperature is still low from the previous night. (Monarchs are more likely to be in trees then.) It is not possible to measure all the colonies at the same time. Instead, it takes two weeks to measure them all. Second measurements have shown the colony size estimate to be quite different. (Why? Think about the other variables we discussed.) Butterflies are not easy to see in a forest; there may be whole colonies that are not known because they move. Different people do the estimates from year to year (as with any long-term monitoring project). Their methods will vary. Funding for research changes from year to year. This affects the time people can spend to plan, do research, analyze, and communicate the results. Technology changes. In 12 years of monitoring monarch colonies, scientists have gone from manual calculations to a computer-based statisical program (ArcView). Copyright 2002-2006 Journey North. All Rights Reserved. Please send all questions, comments, and suggestions to our feedback form