Migrant Bird April Arrivals

by Carl Strang

In contrast to the much earlier flowering dates and insect appearances that I recounted in the previous two posts, April’s birds arrived on dates much closer to those of earlier years. Median dates were 4 days earlier in 2012 than in 2009, 0.5 day earlier than in 2010, and 2 days earlier than in 2011.

One of the April birds that had traveled the farthest was the chimney swift. Following their instinctive schedule, the first of these appeared at Mayslake Forest Preserve on April 19, not much different from 2009’s date of April 24, April 21 in 2010 and April 25 last year.

The medians represent samples of 13, 14 and 13 species in the three comparisons, respectively. The largest range was the comparison to 2009, at 21 days earlier to 26 days later.

Lesser scaup first stopped by May’s Lake on April 5, distinctly later than the dates of 10 March, 16 March and 31 March in 2009-2011, respectively.

The contrast with flower and insect phenology is stark, and indicates how responsive those two groups are to local conditions. These birds wintered well to the south, have no idea of local conditions, and simply follow the dictates of their biological clocks and instincts. I expect to see little difference in May as well.

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