as humans sometimes have regional dialects or accents, birds from
particular areas may have distinctive songs. These areas may
be as small as a neighborhood of singing Indigo Buntings or may span
across a larger region. The boundaries between dialects of
Sparrows are so sharp that a listener can stand facing the Pacific
Ocean at the Point Reyes Bird Observatory and hear one dialect on the
left and another on the right.
Other species have less geographic variation in their songs, such as Black-capped Chickadees, which sing hey-sweetie from Maine to British Columbia. However, on Martha's Vineyard, an island off Massachusetts, the chickadees sing sweetie-hey on the western end of the island, and swesweetie-sweetie on the eastern side. Dialects tend to develop in birds that remain at the same locations where they learned their songs. The distinct chickadee dialects on Martha's Vineyard probably developed because those birds are relatively isolated from those on the mainland.