Friday, October 30, 2015

Carolina (Chickadee) On My Mind

Engines roared as the plane prepared for liftoff. The force pressed me into my seat – upright and with tray table stowed – as we separated from the ground. I peered eagerly through the double-paned windows at the bird’s-eye-view. The grid of Duluth and white-capped Lake Superior (surf’s up!) zoomed by. Damp and brown, with rounded edges, the lakes, forests, and swamps of northern Wisconsin appeared next. Ringing each circular bog (each created by a chunk of glacier that was buried and melted) was a border of bright yellow. The tamaracks were in full fall color.

On the other end of my journey, forested riverways squiggled among a crazy quilt of farm fields outside Raleigh, North Carolina, as we prepared for landing. Green trees seemed oblivious to the imminent onslaught of winter. Descending into a week of sunny-and-75 felt like a trip back to August, and was disorienting. While attending a conference gave me some structure, I still had to navigate this unfamiliar city landscape to find food among the highways and stoplights. Thinking back to all the birds I’d recently watched head south over Hawk Ridge in Duluth, I felt a deeper sense of empathy for the challenges they face on migration.

Happily, on my last afternoon, a friend whisked me away to the beautiful Sarah P. Duke Gardens on the Duke University Campus. Somewhere past Azalea Court and the Dawn Redwood, a birdcall stopped me in my tracks. It was just a simple dee-dee-dee from within a small tree, but it sounded so familiar. Peering through the thick foliage, I glimpsed the black-and-white face of a little chickadee. Instantly, I felt more at home. Black-capped chickadees gurgle at each other over seeds outside my window each morning, and some form of chickadee has always accompanied me on my travels. This Carolina chickadee felt like the local welcoming committee. (Never mind that it was scolding me for being in its territory).

I’m not alone. Across the country, migrating warblers in unfamiliar territory seek out flocks of residential chickadees as local guides. The chickadees pass on information about the best food sources, and are tuned to local threats. Chickadees are such helpful hosts that throughout the winter, many species of birds associate with their black-and-white flocks.

The small winter flocks of both types of chickadees consist of a few mated pairs, and the recent offspring of pairs from other flocks. Young chickadees don’t hang out with their parents; this prevents inbreeding. Each flock has a strict dominance hierarchy for each sex. Watch the birds at your feeders closely – subordinate birds quickly put down their seed and leave if a dominant bird gurgles at them. Despite their gregarious daytime personalities, each chickadee sleeps in its own shelter or cavity.

Besides having slightly different calls, black-capped chickadees are also adapted to colder, harsher winters. The division between the two species seems to be the band of average minimum winter temperature of 17 degrees Fahrenheit. This line – and the boundary between the two species – stretches from New York City to Kansas, with a steep dip south along the Appalachian Mountains in West Virginia and Tennessee. In a 20 mile wide band along the divide, the chickadees hybridize.

Several fascinating research projects have given us a glimpse into this band of illicit romance. Turns out, when females of either species don’t know which male is dominant, they sidle up to the black-capped chap. But when the males interact, Carolinas usually dominate, and females of both species dig that. The resulting hybrids are almost impossible to recognize physically, but their songs are a confusing mashup of both species.

Another incredible discovery is that this band of hybridization has been moving steadily north – nearly a mile a year in some areas – and it follows the trend of rising temperatures. This shift has been occurring for at least half a century, and probably since the retreat of the glaciers that formed our tamarack-ringed bogs.

While northern Wisconsin will remain a stronghold of black-capped territory for many years (our current average minimum winter temperature is 10 degrees Fahrenheit), cities like Chicago, Springfield, and Kansas City may soon be dancing to a different tune. Happily, the warblers and I can still count on chickadees to help us feel at home wherever we go.
Carolina Chickadee Photo by Dan Pancamo

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