By request from my friend Tracy, a former South Texas resident: this is a Black Bellied Whistling Duck! Someone told me not too long ago that they're actually tree ducks (rather than diving ducks like the Ruddy from last week or dabbling ducks like a Mallard) which explains their odd behavior. In my neighborhood, you can see them sitting on rooftops and power lines. I've often joked that they just don't know that they're ducks. If you live in South Texas, you can see and hear them coming. They make a squeaking/whistling noise and in flight, you can distinguish them by their white wing bars. Keep an eye out! I took this picture at South Padre Island's World Birding Center on April 6, 2012.