As a result, virtually the entire population of some raptors fly through a strip of land just 25 miles wide. In a word, no. Scientists believe that birds know when to migrate because as we approach spring daylight gradually lengthens. Changes in length of the daylight activate hormone producing glands in birds. Hormone levels are the actual trigger for migration.
Birds head south in the fall even though food is still plentiful.
Hummingbirds leave in September although flowers are still in bloom and feeders are available. Warm your heart on these cold winter nights with the knowledge that in just a few short weeks a little bit of the tropics will be winging their way north to your backyard. Click this link. Easy Site Navigation E-mail Questions or Comments by clicking the leaf. 1999 by Wild Bird Kalamazoo.