Some 500 dead and dying birds fell onto a Louisiana highway on Monday, just three days after a similar incident in Arkansas. The Louisiana Department of Wildlife and Fisheries [said] that necropsies on some birds indicated many exhibited traumatic injuries." Two dozen of them had head, neck, beak or back injuries. In Arkansas, preliminary tests showed the blackbirds there, as many as 5,000, died after massive trauma. "The birds suffered from acute physical trauma leading to internal hemorrhage and death," the Arkansas Game and Fish Commission said in a statement. "There was no sign of chronic or infectious disease." The injuries were primarily in the breast tissue, with blood clotting and bleeding in the body cavities. Dr. George Badley, the state's top veterinarian, told NBC News that the birds died in midair, not on impact with the ground. That evidence, and the fact that the blackbirds fly in close flocks, suggests they suffered some massive midair collision, he added. That lends weight to conclusion that they were startled by something. The commission noted that "loud noises were reported shortly before the birds began to fall from the sky," adding that blackbirds seldom fly at night. The commission also is trying to determine what caused the deaths of up to 100,000 fish over a 20-mile stretch of the Arkansas River near a dam in Ozark , 125 miles west of Beebe. The fish were discovered on Dec. 30.