by Carl Strang
On Friday I shared this year’s flowering phenology through the end of April. There have not been enough first appearances of insects yet to make a comparison to previous years, but birds have been arriving at Mayslake Forest Preserve for more than a month. Most of these are species that winter in the southern U.S., and so are capable of tracking the weather conditions and adjusting their migratory jumps accordingly. Consequently the dramatic differences we see among years in plants’ first flowering dates are not reflected in the arrival dates of birds.
That said, the median difference between this year and last for the 31 species I could compare was 7 days later in 2013. One week, compared to nearly 5 weeks for first flowers, seems small, though it should be added that the range of arrival date differences was large, from 70 days earlier to 37 days later.
That 7 days’ difference was the largest in recent years. Median arrival dates in 2013 were 3 days later than in 2011, 2.5 days earlier than in 2010, and 5 days later than in 2009 (34 species in each case). All the ranges were large, in fact all were larger than for 2013 vs. 2012. Nevertheless, it would be hard to build a case that bird arrival dates varied much from year to year.