In a 1999 series of dives, a falcon named Frightful was released from a Cessna 172 at 17,000 feet and was reportedly clocked at 242 mph (389.46 km/h), according to Guinness World Records. To measure Frightful's speed, a 113.4-gram computer chip from a skydiver's recording altimeter was fastened to her tail feathers, and the distance she fell in a time interval was measured. Altimeters were also worn by a person named Franklin and by a cameraman who skydived with Frightful, and one was on the lure released to simulate prey. The data from all four devices were compared after the dives.

Some ornithologists have doubted the Frightful dives because they did not recreate natural conditions, such as starting at a higher altitude than peregrines would normally dive from. Guinness World Records says the Frightful figure came from experimental dives, which suggested that peregrines might reach higher speeds than the estimated terminal velocity of about 320 km/h. So the 242 mph figure is a reported speed from an experiment, and some ornithologists doubt it.

Other work looked at how a falcon's body handles the air. A 2014 study in PLoS ONE trained falcons to dive in front of a 60-meter dam wall. Wind-tunnel tests with a life-size model falcon showed regions where air flow separates from the body, and pictures of the diving falcon showed small feathers popping up in the same regions. The authors of the dam-wall study think the pop-up feathers most likely act as passive flow control units that prevent flow separation. In that study the falcon pulled out of its dive. Its maximum acceleration was 11.5 meters per second squared, nearly 1.2 times the acceleration of gravity.

The peregrine's own history is a measured one too. In the middle of the 1900s the pesticide DDT made peregrine falcon eggshells thin, and the eggs broke while the parents sat on them. The United States banned the use of DDT in 1972. By August 1999 The Peregrine Fund and others had released over 4,000 captive-raised peregrine falcons in 28 states, after 28 years of effort. As of November 2026, Audubon says current peregrine falcon populations appear to be stable or increasing.

A peregrine falcon often watches for prey from a high perch, such as a cliff or a tall tree. In cities it nests on ledges of tall buildings and eats pigeons. Survival through the first year of life is estimated at 40 percent, and adult survivorship at 70 percent. Pairs often last through many breeding seasons, and some nest sites are used again and again for many years.

Words to know

• altimeter: height meter
• ornithologists: bird scientists
• terminal: final
• lure: fake prey
• altitude: height