American robins now migrate 12 days earlier than in 1994: New GPS data show birds adjust to shifting snow conditions as climate warms 

A new study concludes that robin migration is kicking off earlier by about five days each decade. The study is also the first to reveal the environmental conditions along the migration route that help the birds keep up with the changing seasons.

Source: American robins now migrate 12 days earlier than in 1994: New GPS data show birds adjust to shifting snow conditions as climate warms — ScienceDaily