Why
Do Daily Monarch Counts Go Up and Down?
Analyzing Data From a Fall Migration Roost
Contributed by Paul Viger, Campbell, Minnesota
During
fall migration, some lucky people have thousands of monarchs pause
in their yards at overnight roosts. Mr. Viger of Campbell, MN is
one such person. Each day he counts the monarchs, tags them, and
records information about the wind and weather. As they do each
year, the monarchs stayed for almost 3 weeks in fall 2001. He watched
their numbers rise and fall each day, and noticed an interesting
pattern. You can see it too if you look carefully. What might be
causing the daily changes? (Click
graph for a larger version.) |