The National Transportation Safety Board suspects a bird strike could have been the cause of a crash involving a 1975 Cessna Citation I on 4 March after taking off from Wiley Post Airport in Oklahoma City.

The Board's invstigators have taken residues from the horizontal and vertical stabiliser of the Cessna Citation I and these have been sent to an ornithologist at the Smithsonian Institution in Washington DC for identification.

Eye witness accounts suggest that the aircraft flew into a flock of birds as it climbed through 3,100ft (937m) and that white bird body parts fell to the ground shortly after the crash.

Footage from a security camera at a power company located approximately 0.8km (0.5 mile) southwest of the accident site reveals "that the airplane descended to the ground while in a near vertical position" while emitting a smoke contrail, according to the NTSB's preliminary report.

One witness, a former US Air Force crew chief, reported grey smoke trailing from the right Pratt & Whitney Canada JT15D-1 engine. The crew made no distress calls, say NTSB investigators.

According to the FAA, the number of wildlife strikes reported annually in the USA has quadrupled over the past 17 years, rising from 1,743 in 1990 to 7,089 in 2006, with 97.5% of those strikes attributed to birds.

Over the same period, the FAA says that five of seven wildlife strikes that caused nine human fatalities were attributed to unidentified species of birds. The FAA says the aircraft components most frequently damaged in collisions with birds are engines.

The Smithsonian's Feather Identification Lab is called upon to investigate approximately 3,000 bird strikes per year, attempting to identify the type of bird involved based on carcasses, feathers or most recently, DNA samples sent to the lab.