National Geographic News
For some, the magic moment happened a week ago. For others, it happened just the other day. Many are still waiting, but some morning soon they too will wake to the lilt of a backyard bird pleading for a mate.
Chickadees will whistle "Phoebe," nuthatches will honk like a tinny horn, titmice will screech "Peter, Peter, Peter," and woodpeckers will hammer out their heart's desire with their beaks against hollow branches.
"These are all winter birds. It's still winter, but the light, the changing light, has a hormonal trigger, and that starts the birdsong," said John Hanson Mitchell, an editor with the Massachusetts Audubon Society in Lincoln and author of A Field Guide to Your Own Back Yard.
Mitchell said the singing of the winter-resident birds is among the first signs that spring is around the corner. Birders begin to report the sounds in the middle weeks of February.
John Dunning, an ecologist at Purdue University in West Lafayette, Indiana, said birds have photoreceptors in the bases of their brains that record the length of the dark period each day. As the darkness shortens, and as days lengthen, birds get spring fever.
"The photoperiod is very standard from year to year," he said.
"Days lengthen at a regular pace." Therefor, using the photoperiod to gauge the season is more reliable than, say, following cues such as an emergence of insects or a freshly sprouting plant, which could easily be fooled by a midwinter warm spell, Dunning added.
The first birds to sing of the pending arrival of spring are the same birds that never left for the winter, Mitchell said. In Massachusetts winter residents include chickadees, nuthatches, woodpeckers, titmice, cardinals, and mockingbirds.
"They have millions of years of evolution learning to survive the winter," Mitchell said. "They're here because they know how to do it. Other species don't know how to do it, so they go south."
The winter residents survive by adapting to the available food. Nuthatches will scour the crevices of tree bark in search of insect eggs and grubs, for example. Chickadees and titmice feast on seeds. Woodpeckers hammer away at trees to fish out insects sleeping away the winter.
"[Woodpeckers] are well adapted to drill and excavate insects from deep within trees," Mitchell said. "They must look at a little pinhole and say, There must be something in thereand then they drill it out."
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