Scott Wright: Impact trauma is a term that we use to differentiate different things that might have caused the birds to appear the way they do when we conduct the necropsy, which is an autopsy of animals. And what we look for are specific appearance of organs and blood and so forth that might be where it’s not supposed to be and that sort of thing, as a result of the birds striking either a flat or blunt surface as opposed to a sharp surface. So impact trauma in this case means that the birds struck something that was blunt or flat.
What we looked for are tears in the organs, some broken bones, and hemorrhage, which means there’s free blood in places where we wouldn’t normally find it like within the body cavity. All of these are indications of type of trauma, in this case, from blunt surface.
See more. Stolen from: http://www.usgs.gov/corecast/details.asp?ep=140