Presbyornis, whose name you cannot find the meaning to anywhere online, is a bird with an interesting image. The image of the skeleton, and there were many to chose from but I liked this one more than the rest for its completeness and locomotive depictions, in contrast to the human skeleton is completely the property of Scott Hartman. This image is from the linked blog article from yesterday, to be specific, and shows, in good detail the attributes which allowed for Presbyornis to both originally be mistaken for a flamingo's ancestor and for the later reassessment as the ancestor of the modern duck. The body is very easily identifiable as that of a bird that wades more than bobs along on the water floating due to the large long shin and ankles (blue and green bones). While this is certainly not very duck-like, it does explain the anatomical misinterpretation very well. The bill, however, is a clearly duck-like trait (flamingo's bills curve downward and are adapted for sifting and filtering more than dabbling). The bill of Presbyornis is very well suited toward this dabbling method of feeding as they can crop vegetation under the water or scoop up small items at the surface without scooping in large amounts of water.
Living at the water's edge, however, would have its dangers then as it does now to be sure. Like ducks, and the cranes and flamingos it is not related to, Presbyornis was a species of bird with the ability to fly. Crocodiles, like that in the image from Currie and Sovak's book, were of course not the only danger of the water, but the ability to vertically escape is an advantage over pretty much all land and water based predators as most can only jump so far. Therefore, unlike our earlier discovery, Hesperornis, Presbyornis had a distinct evolutionary advantage over some earlier waterfowl in that they had that ability to take to the wing. Hesperornis more than likely tried to outrun opponents, an easy task in water, but the long legs of Presbyornis, while well suited to taking long strides, were not necessarily built for running and certainly not for strong swimming habits. Additionally, having long legs, in the event of a much needed and quick escape, would add not only muscle and leverage to the spring into the air but their height makes the point of attack from below, such as would be the case for this crocodilian, that much longer to solidly reach in order to foil the escape attempt of the bird. Basically, longer legs means Presbyornis was farther, literally, from the dangers ambushing it from below. Perhaps not much, but enough that, if the predator missed clamping down on the leg, the bird would have enough warning to launch itself into the air before its body could be chomped down on. That's a lot of ifs ands and buts, however, nature is complex. Regardless, the image of the attack does effectively show the ability of Presbyornis to evade a predator using its wings and legs.
What about flight, though? Actual physical flight for the two species in Presbyornis wouldn't look much like a duck's flight. It couldn't, not with long legs like that. A duck in flight tucks up its little legs under its body extending them into the water upon landing, using them as water breaks; geese do the same thing. Animals that fly with their legs out include, here we go again, flamingos, cranes, and herons. So why would an animal that stands like a crane, flies like a flamingo, has been depicted standing like a heron, and has the body shape of a wading bird, overall, be considered the ancestor of a duck? Is it truly just off of that bill? The answer is, of course, no, it is not simply the bill. Ducks, and other anseriformes like geese and swans, and Presbyornis share many characteristics with one another. It is these many characteristics which have in the past also led to speculation that Presbyornis is a transitional genus between wading shorebirds and anseriformes. As of now, however, it is simply considered a very early ancestor of ducks, geese, and swans.