Male great reed warblers may be practicing how to woo
5:00PM, FEBRUARY 4, 2016
WHY SING IN WINTER Marjorie Sorensen, tracking bird movements in a seasonally flooded valley in
studying why great reed warblers (one shown, right) overwintering there sing so
Europe’s great reed warblers (Acrocephalus arundinaceus) and some other male long-distance migrants sing extensively when overwintering in sub-Saharan Africa, says Marjorie Sorensen, now at
“Why are they doing this when they’re thousands of kilometers from any possible
breeding opportunity?” Frankfurt
Singing seems costly. Reed warbler songs — “very harsh-sounding and creaking,” Sorensen says — are changeable compositions made up from a male’s repertoire of some 40 to 60 sounds. Tests find that singing demands about 50 percent more energy than reed warblers spend resting. Plus, singing cuts into foraging time and risks catching predator attention.
Warbler in winter
Biologists largely expected the wintertime musical extravagance to be territory defense. But the birds creak variations of courtship serenades instead of shorter territorial anthems, Sorensen and her colleagues report in the March American Naturalist. And instead of squabbling over their patches, the warblers freely crisscross the landscape. Nor did testosterone elevation left over from the previous breeding season play a role — levels had dropped to winter lows.