May Phenology: Migrant Birds

by Carl Strang

May is the main month in northeast Illinois for arrivals of migrating birds that spent their winter in the tropics. I compare first observation dates of each species between years as part of my phenology study at Mayslake Forest Preserve. As I noted a month ago, birds are less influenced by weather than are insects and plants, which form the other two legs of my phenological comparisons among years. This was the case in May as well.

The first chestnut-sided warbler to appear at Mayslake this year was representative of the whole, arriving 4 days later than in 2010, 2 days later than in 2009.

Median arrivals in 2011 were not much different from those of the previous two years. The median vs. 2010 was 3 days later, and 2 days later than that for 2009. Differences were more dramatic for plants and insects, as I’ll show tomorrow.

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