First Song Dates, 2011

by Carl Strang

As I wrap up the year’s singing insects field study I am interested in making summary comparisons to earlier years. Last week I reported on block counts. Today’s focus is on first song dates.

The dog-day cicada’s first song date of July 4 was the fourth-earliest for that species among my 6 years of observations.

I have 6 years of first song date records for 23 species. None of the 2011 dates were earliest for a species, 1 was second-earliest, 5 were third-earliest, 10 were fourth-earliest, 3 were fifth-earliest, and 4 were latest. This was different from the expected even distribution of 3.8 in each category, and it produced a χ2 test statistic of 16.54, indicating a statistically significant departure from the expected (P<0.01). The biggest contribution to the χ2 value was from the middle-of-the-road fourth-earliest category, suggesting this was an unremarkable year for starts, neither early nor late.

The snowy tree cricket was another species whose first song date was fourth-earliest. The July 29 date was 16 days later than in 2010.

Focusing on the readily observed species, for which I have some confidence that my observations have strong validity, first song dates were a median of 9.5 days later in 2011 than in 2010 (n = 26 species, range 17 days earlier to 26 days later), and 2.5 days earlier in 2011 than in 2009 (n = 24 species, range 24 days earlier to 22 days later). Those values are comparable to the late flowering phenology pattern I observed at Mayslake Forest Preserve this year, which in turn reflected the soil-chilling February blizzard and the cool spring.

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