Friday, January 25, 2008

Rusty Blackbird

Yesterday, Jeff Mollenhauer, Audubon South Carolina’s Director of Bird Conservation, attended a workshop about Rusty Blackbirds (Euphagus carolinus). You aren’t alone if you are wondering what a Rusty Blackbird is and why are they important enough to draw researchers from more than five states. "Aren’t they just a blackbird? Good for baking in pies?" Actually, some researchers have dubbed them as the “un-blackbird” because of their behavior differs from that of their close relatives. Their cousins, Red-winged Blackbirds (Agelaius phoeniceus), cowbirds, and grackles, can often be found feeding in farm fields, lawns, backyards, and other open areas, while the Rusty Blackbird prefers to feed in forested wetlands on large invertebrates such as dragonfly or damselfly larvae and even small fish. Their behavior is similar to a shorebird, in that they walk along the edge of ponds or puddles flipping over leaves in search of prey and occasionally even wading out into the water. Rusty Blackbirds are also much quieter and shier than their loud, raucous cousins making them difficult for scientists to study. (Rusty Blackbird. Credit Donna Dewhurst, USFWS)

Over the past 40 years Rusty Blackbird populations may have declined by as much as 98% based on results from the Breeding Bird Survey and Christmas Bird Count. There are an estimated 1.4 million Rusty Blackbirds remaining in the world. This may seem like a big number, but it is pretty small compared to the 70 million that roamed the earth forty years ago. Scientists have not yet determined the source of this precipitous decline, but are investigating habitat loss on both the breeding grounds in the boreal forests of Canada and wintering grounds in the southeastern United States. South Carolina boasts some of the highest numbers of wintering Rusty Blackbirds on the Atlantic Coast. Among the best sites to see Rusty Blackbirds in South Carolina are Donnelley WMA, Santee NWR, Savannah NWR, Magnolia Plantation, and Lake Conestee Nature Park. Rusty Blackbirds can be found in South Carolina from November to April.

Another potential cause of their decline may be mercury contamination of streams and wetlands. Studies have shown that insectivore food webs biomagnify mercury more than fish food webs. Since the Rusty Blackbird is feeds primarily on aquatic insects they may be more susceptible to mercury contamination than fish-eating birds. As we have reported previously, we are particularly concerned about mercury pollution in the South Carolina, since many of the waterways in the coastal plain already have fish consumption advisories due to elevated levels of mercury. In fact, mercury contamination is known to be high right here in Four Holes Swamp. About 50% of the mercury in our streams is probably attributable to natural sources, but the rest is mercury pollution from man-made sources. Coal-fired power plants are known to be a major source of mercury pollution. A recent study in eastern Ohio conducted by the EPA and University of Michigan, determined that coal combustion plants caused 70% of mercury pollution within the Ohio River Valley. Their analysis also indicated that much of the contamination was from local or regional sources.

So if you see a Rusty Blackbird, count yourself lucky and wish them well as they prepare for their trip north.

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