May Bird Arrival Phenology

by Carl Strang

May is the last month in which I track migrant bird arrival dates at Mayslake Forest Preserve, as the spring migration is practically concluded. As has been the case this spring, median bird arrival dates have not been nearly as different from previous years as those for first flowers or insect appearances. The 22 species I could compare between 2012 and 2011 were a median 4.5 days later this year, ranging 9 days earlier to 38 days later. The median difference from 2010 was exactly 0, or no difference, with a range of 8 days earlier to 19 days later for 20 species. Finally, 21 species arrived a median 5 days later than in 2009, ranging 10 days earlier to 26 days later.

The rose-breasted grosbeak was fairly typical, the first arriving at Mayslake on May 4 this year, May 2 last year, May 4 in 2010 and April 27 in 2009.

As I mentioned when summarizing data on bird preferences for buckthorn vs. oak woodlands, this year was characterized by a number of migrant species bypassing Mayslake altogether, so there were many for which comparisons could not be made.

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