February 18, 2014, continued. After admiring the persimmon, I spot movement back in the partially-flooded oak flats behind the tree and see a flock of 150 plus rusty blackbirds feeding in the leaf litter. Unlike some other leaf tossers – robins and hermit thrushes – rusties don’t mind getting wet and will wade almost to their bellies poking at debris and turning leaves in the water. They are successful too, at least the ones I watch, which are gobbling up food morsels that appear to be some sort of invertebrate.
Rusties are a little different from your average blackbird. They are winter visitors in South Carolina, breeding far to the north in wet boreal forest and muskeg country. Unlike most of their blackbird kin, the rusty diet leans more to the animal side. Rather than feeding on waste grain in upland fields, rusties take to the swamps and bottomlands in winter. For whatever reason rusty blackbird populations have declined precipitously since the 1960s, down eighty to ninety percent according to some accounts, and biologists are scrambling to figure out why.
At Congaree the number of rusties on the Christmas Bird Count has been relatively low for the most part, with only twelve of the past twenty- one counts reporting any of the blackbirds at all, and most of the number counted was less than two dozen. However, there were two good consecutive years, in 2012 and 2013, when birds in the low hundreds were reported.
As the early afternoon continues to warm up, I hear frog sounds coming from the flooded oak flats. They belong to male upland chorus frogs getting an early start on attracting lady chorus frogs so they can perpetuate the species. The call is a perfect rendition of a thumb running down the teeth of a pocket comb. Frog taxonomy has changed a lot since I took herpetology forty-five years ago. Back then the upland chorus frog’s scientific name was Pseudacris triseriata; now it is P. feriatum. The specific epithet triseriata is now used to describe a closely-related group of chorus frogs found throughout the South, at least two of which may be separate species.