Comparing Monarchs in the Migratory Generation

We have only made the kinds of comparisons of monarchs at different times during the migratory generation over one year. These comparisons were only made in three different times and locations. Clearly, since this generation lives up to eight or nine months, and can cover up to 3000 miles during this time, it would be possible to study it in much more detail. Think about the following questions, and join a future discussion (coming soon!) of possible answers. If you’d like, you could become part of a more detailed study!

1. What could we learn by weighing the monarchs at different times during the migratory generation?
2. What could we learn by doing a detailed study of sex ratios over the course of the whole migration?
3. What could we learn by comparing the timing of migratory monarchs’ arrival in different places over the course of several years?
4. What could we learn by comparing monarch mass, winglength or wing condition over several years?

To join in on the discussion, email us with your thoughts about the previous questions.  We will post them as soon as possible.  Please include the question you are discussing in the subject heading.  

Comparing Monarch Winglengths throughout the Breeding Season

We collected winglength data on monarchs for several seasons before we even looked for a pattern over time, and were very surprised to learn that monarchs got bigger over the course of the summer. This is a good example of how many things you can learn by collecting lots of data; you may find patterns you had never anticipated. Since we just found this pattern ourselves, we have not begun to study the factors that may be causing it. Please let us know if you learn anything new about this!

Winglength, unlike any of the other characteristics that we study, is totally determined by conditions that the immature stages of monarchs experience, since monarchs’ wings do not grow during the adult stage. Thus, we need to study these stages in order to understand this pattern. The pattern could be caused by abiotic factors, like temperature, daylength, or humidity. It could also be caused by biotic factors, like exposure to parasites, milkweed species, or milkweed quality (age, condition, size, or chemical composition).  Think about the following questions, and join a future discussion (coming soon!) of possible answers. If you’d like, you could become part of a more detailed study!

1. What are several factors that might affect monarch size, and vary over the course of a summer? How could these factors affect monarch size?
2. How could you study the effects of these factors?

To join in on the discussion, email us with your thoughts about the previous questions.  We will post them as soon as possible.  Please include the question you are discussing in the subject heading.  

Sex Ratio Studies

When we study sex ratios, we are concerned with both actual sex ratios, the proportion of both sexes in the actual population we are studying, and capture sex ratios, the proportion of both sexes in the sample of the population that we actually measure. It is often very difficult to determine actual sex ratios in a population of animals, because one sex may be easier to catch or more visible. Here are some things to think about regarding this and related issues. If you’d like to discuss any of these questions, just click on them, and send your thoughts to us!

1. How would your estimate of monarch sex ratios be off if it was easier to catch females? What other things could make your capture sex ratio different than the actual population sex ratio?
2. Assume that you have a study site where there are large patches of milkweed, and separate large patches of flowers. There are monarchs in both of these sites. What reasons could lead to biases in your capture sex ratio? If you caught more males in the milkweed and more females in the flower patches, what could be possible explanations for this pattern?
3. Let’s say you sample monarchs as they come to your garden in September. In the first week, you catch 23 males and 12 females. In the second week, you catch 35 males and 32 females. In the third week, you catch 15 males and 26 females.

1. Do any of these samples have significantly biased sex ratios? (check our Basic Stats section for directions on how to test this)
2. What could explain a pattern like this?

To join in on the discussion, email us with your thoughts about the previous questions.  We will post them as soon as possible.  Please include the question you are discussing in the subject heading.  

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