First and Last Song Dates

by Carl Strang

I have one last topic from 2009 to report in my singing insects study. I now have enough years (4) of data to look for patterns among species in first and last song dates. I am reasonably confident that my records for 20 species are good enough to include in this comparison. The object of this analysis is to see whether this year’s singing insect season is relatively early or late compared to other years.

First song dates at first glance seem to point to 2009 as a relatively late year compared to 2006-2008, with the earliest song date recorded for only one species, second-earliest for 3 species, second-latest for 9 species and latest for 7 species (a random distribution would have 5 in each category). A chi-squared contingency test produces a test statistic value of 8, however, not quite high enough to indicate statistical significance (P > 0.01; it is perhaps worth mentioning that if I were content with a 5% chance of error rather than 1%, statistical significance would have been indicated). The last song dates I noted for the 20 species in 2009 were closer to an average or random pattern within the 4 years, with 5 earliest finishes, 6 second-earliest, 3 second-latest and 6 latest. The test statistic consequently is very small here, at 1.2. This is only the first year of this analysis; I’ll be interested in seeing what emerges in future years.

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