Wood Thrush Symphony

April 26, 2014, conclusion. I continue my paddle down Cedar Creek and about 7:45 AM, as I approach “Garrick Hill,” a high bluff on the north side of the creek, I hear a sound that makes me stop in mid-stream. It’s the most beautiful song in the bird kingdom in my humble opinion, the fluting melody of a wood thrush, coming from the woods on top of the bluff. I immediately paddle over to the north bank and walk up the steep bluff to better hear it. The thrush is singing nearby from a stand of young, mixed pine-hardwoods and delivers its virtuoso performance for nearly fifteen minutes before stopping for a break. I actually never see it since I’m afraid I’ll spook it if I get too close or make noise searching for it.

Words don’t do justice to this exquisite bird song, but a series of liquid flutes rising and falling like water is about as close as I can come. The setting for this enchanting music is perfect, too – a cool, spring morning with a low, April sun lighting up the woods still in dawn’s shadows, and with a light touch of breeze. This is about as good as it gets, and right now I feel like the richest, and luckiest, man in Richland County, if not South Carolina. But it is also saddening to me that so few people will ever enjoy and appreciate this natural bird symphony.

This has not always been the case. When I first moved to Forest Acres as a young boy the wood thrush was nesting in vacant wood lots along Forest Drive near our home, about where the Bonefish Grill and McAlister’s Deli are now located. You could sit on the back porch on a summer’s evening and hear their vespers. Wood thrushes were almost a yard bird then. Unfortunately, they have since retreated to large tracts of forest land miles away from the suburbs and have shown some of the most dramatic, long-term population declines of any songbird in North America. Along the way, most Americans have been robbed of one of nature’s most beautiful sounds.

Reasons for the sharp decline of wood thrush populations are complicated and not entirely understood, but we know that they, like many of our so-called Neotropical migratory birds – warblers, vireos, flycatchers, buntings, orioles, tanagers, and others that nest in North America and overwinter in the tropics – are sensitive to forest fragmentation. Fragmentation occurs when forest and farmland are subdivided and broken up into parcels for homes, shopping centers, highways, industrial sites, wide power line rights-of-way, and other development. Once a forest tract becomes too fragmented, it starts losing many of its nesting birds.

The really insidious thing about forest fragmentation is that although wood thrushes, like many Neotropical migrants, have breeding territories of only a few acres, they will abandon forest fragments of suitable habitat many times larger. Although figures may vary according to species, researchers have determined that for many songbirds of eastern forests, 250 acres is a minimum size to maintain stable populations of most species.

I suspect what was happening to my Forest Acre wood thrushes sixty years ago was what wildlife ecologists call the “source-sink phenomenon.” In my case, the wood lots on Forest Drive  probably supported a wood thrush “sink” population, i.e. due to small parcel sizes, with perhaps more predators per unit area, including small boys that robbed their beautiful turquoise-blue eggs for their collections, the thrushes were not producing enough young to maintain the population. They were in turn, “subsidized” by a surplus of thrushes produced from larger forest parcels with better habitat and relatively fewer predators – the so-called “source” population. The Forest Acres landscape of sixty years ago was vastly different from today’s: Trenholm Plaza was not even built (nor was Richland Fashion Mall); there were virtually no housing developments beyond Dentsville; Fort Jackson and its mostly wooded environment came right down to Gills Creek; and there were far fewer homes and development than today.

The Congaree National Park, with its huge number of breeding songbirds, probably serves as a  source population of birds to colonize and subsidize forest fragments and woodlots in adjoining areas. Surprisingly, however, wood thrushes rarely breed in the Congaree floodplain, despite what appears to be prime habitat. It’s a puzzle to me why they don’t; in other parts of their range wood thrushes sometimes nest in the higher parts of floodplains, especially the levee forest along the river’s edge. At Congaree they are mostly upland nesters, typically along the swamp edge and bluffs that support hardwoods and mixed pine-hardwoods with an understory of shrubs and and saplings.

Wood Thrush photo courtesy Heyward Douglass