Bird Symphony Reprise

By September, the southern migration of New Hampshire song birds is underway. With breeding and chick-rearing duties fulfilled, songbirds adopt a more leisurely pace. Colorful breeding plumages are molted to drab fall colors creating confusion in identification of fall warblers.

Once carefully defended spring breeding territories are now abandoned. Birds that exhibited tight habitat affinities during the nesting season are now less fussy. In spring time, a Black-throated Blue Warbler which favors hardwood forest is now just as likely to appear in a parking lot in Manchester.

Researchers recently discovered that songbirds adopt a more leisurely pace during the fall migration than during the spring. They mounted miniature tracking devices on wood thrushes and purple martins breeding in Pennsylvania to track the birds' autumn migration.

They study found that songbirds' overall migration rate was two to six times faster in spring than in fall. A purple Martin that took 43 days to reach Brazil in the fall returned to its breeding colony in only 13 days in spring.

A nostalgic autumn sound is the faint reprise of the spring symphony. In response to falling light and hormone levels, birds sing a fragmented farewell. Amid the metallic call notes- the chips and ticks of feeding and location calls- are occasional snippets of spring song, recognizable even if raspy or partially rendered. Diagnostic songs of sparrows are reprised briefly in the early morning along their fall migration routes.

The falling notes are a bittersweet parting: more sweet than bitter.