Cuckoos Arriving Earlier!

By Roger Tabor

I invited the BNA Annual Conference delegates to help me plot during the conference the first arrival dates of cuckoos from a large sample of data spanning a significant part of the 20th century previously extracted from the BNA phenological archive. I subsequently calculated and plotted the yearly means of the records. The BNA has been making phenological records since its formation in 1905. This provisional graph shows that over the 50 years from 1930 to 1980 the cuckoo arrival times heard and recorded by BNA members became progressively earlier by some 10 days. This finding on our most familiar avian migrant dubbed the herald of Spring is consistent with the proposition that climate is being affected by global warming.

Graph showing the first arrival of cuckoos, 1915–1979