A 2014 study in PLoS ONE says peregrines can reach more than 320 km/h in a dive, but that such speeds make exact measurements of free-flying falcons hard. So the authors trained falcons to dive in front of a 60-meter dam wall. A stereo high-speed camera system recorded 35 dives. The 3-D flight path of the falcon was reconstructed from the images, and one dive by a falcon with a mass of 0.5 kg was analyzed in detail.

The highest speed measured in the dam-wall study was 22.5 meters a second, about 80 km/h. The authors say the dam was low, so the falcons only reached up to 80 km/h in their experiments. That is a measured number from the experiment. The same study says a peregrine reaches up to 150 km/h in horizontal flight.

How does a peregrine find its prey from far away? Peregrines flying at distant prey follow a curved path called a logarithmic spiral. Tucker and colleagues found wild peregrines holding their heads straight and flying curved paths toward prey from distances of up to 1500 meters. A peregrine has to turn its head about 40 degrees to see prey straight ahead with the sharpest part of one eye, the deep fovea, but a turned head adds drag and slows the falcon down. Tucker tested raptor models in a wind tunnel and found that turning the head works like an air brake on an airplane, because it increases drag. He found it is faster for the birds to dive along a curved path with the head straight, with the prey at 40 degrees, until close enough to see it clearly straight ahead.

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 1999 the peregrine falcon was taken off the United States list of endangered species, after its numbers had grown back. Biologists raised thousands of young peregrine falcons in captivity and released them into the wild.

Peregrine falcons are found worldwide except for rainforests and cold, dry Arctic regions, and they have also colonized urban areas. Survival through the first year of life is estimated at 40 percent for peregrine falcons, and adult survivorship at 70 percent. A healthy falcon that survives lives an average of 13 years. Peregrine falcons form pairs that often last through many breeding seasons, and both sexes have a strong attachment to previous nesting sites.

Words to know

• fovea: sharp-sight spot
• drag: air resistance
• stereo: two-camera
• raptor: bird of prey
• colonized: moved into