(7NEWS Viewer/KMGH/ABC News)

A United Airlines Boeing 737 struck a bird as it descended into Denver International airport Tuesday morning.

Flight 1475 landed safely at 9:09 a.m. and was escorted to a gate. The plane was flying from Dallas/Ft Worth to Denver. Photos show a large hole in the nose of the plane.

The plane's pilots were aware of the bird strike and declared an emergency.

There were 151 passengers on board but there were no injuries, Christen David, a spokeswoman for United Airlines, told ABC News.

The bird's remains, recovered from the aircraft, will be analyzed by experts from the Smithsonian Institution in Washington, who will help identify the species.

Currently, airliner engines have to be designed and demonstrated able to ingest a four-pound bird without endangering people on the plane, according to Paul Eschenfelder, an adjunct professor at Embry Riddle Aeronautical University. Eschenfelder says that none of the engines flying are designed or built to survive an ingestion of an eight- to 15-pound bird.

The number of animal strikes reported annually has increased from 1,793 in 1990 to 9,622 in 2010, with birds involved in 97.2 percent of strikes, according to the Federal Aviation Administration. Seventy percent of those strikes occurred when the aircraft was at less than 500 feet elevation, according to the United States Department of Agriculture.

Birdstrike.org estimates that wildlife strikes cause more than $600 million in damage to U.S. civil and military aviation annually. According to the organization, more than 219 people have died worldwide as a result of wildlife strikes since 1988.