Responses to Challenge Question #8:
Those Florida Winters

Last time you calculated the number of days on the wintering ground for the HY2005 chicks as 106, the shortest time in five years of data. Sixth grade homeschooler Marcus gave you Challenge Question #8:

• "It appears that there is a trend of the number of days on the wintering grounds [for Eastern flock] getting shorter. Are there any ideas on why this may be?"

Marcus did some great thinking about factors that could affect the length of the Eastern flock's stay on the wintering grounds. He wondered whether they are heading north earlier because of earlier seasonal warming or because the cranes are learning that there is less available nesting habitat. Nick and Kathryn from Iselin Middle School also thought that global warming could shorten winters and send cranes packing earlier. Good reasoning!

Crane Biologist and Expert Tom Stehn

The analysis of the WCEP whooping cranes spending a shorter winter in Florida over the past 5 years might be meaningful if the ultralight arrived in Florida on the same day each year. But the ultralight's arrival is partly determining the length of stay on the wintering grounds. The ultralight's arrival, however, depends not only on when the migration leaves Wisconsin, but also on the weather en route. Thus, to me, the students have done a good job compiling data and calculating length of stay, but conclusions aren't meaningful. It might be meaningful if the departure date from Chassahowitzka was getting earlier and earlier every year.

And we add: You can see the annual departure dates listed here. While it is interesting to keep track of days on the wintering grounds, we have learned something important! We need to look at all the variables before deciding if it's a meaningful conclusion. Which variables would need to be controlled in order for the conclusion to be meaningful?

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