William Rhein's Film of the Imperial Woodpecker, Durango, 1956

The imperial woodpecker was the largest woodpecker known. Raven-sized. About 2 ft tall. Much bigger than its relative, the ivory-billed woodpecker. It was mostly black, with large white wing patches and an ivory-coloured bill, and it lived in the high pine forests of Mexico's Sierra Madre Occidental.

William L. Rhein was a dentist and amateur ornithologist from Mechanicsburg, Pennsylvania. According to Tim Gallagher, his ambition was to make the first film and the first sound recordings of the bird. He paid for his own expeditions. 1953. 1954. Then a third trip, in 1956.

Southern Durango state. Old-growth conifer forest on gently rolling ground, 2,700 to 2,900 m up. Many large trees. Many dead ones. Rhein was camping in a remote location, with companions later named as Richard Rauch and Heintzelman.

Then she was there. A single adult female, her pointed crest all black. Rhein filmed her with a hand-held 16 mm colour camera, from the back of a mule. She hitched up the trunk of a Durango pine, one of the thickest around. She climbed quickly and pecked at the tree four times. Bark chips flew as she hunted for hidden prey. Then she launched from a treetop with deep, powerful wing strokes and flew out of sight. Years later, Rhein put it simply. "Like a great big turkey flying in front of me."

The reel ran 2,041 frames. About 85 seconds. The mule made the footage jerky, and Rhein called it "very poor footage." Gallagher thought he "was embarrassed by it."

The film surfaced through a paper trail. Martjan Lammertink of the Cornell Lab of Ornithology found a mention of it in a 1962 letter among James Tanner's correspondence in the Cornell archives. He tracked Rhein down and saw the film in 1997. Rhein died in 1999. His nephew, Ronald Thorpe, later gave the original reel to the Cornell Lab's Macaulay Library, where it was restored and digitised.

March 2010. Lammertink and Gallagher returned to Durango with Pronatura Noroeste. Working from the 1956 landmarks, they relocated the film site, east of the old lumber camp of Los Laureles and near the village of Guacamayita. The forest had been logged multiple times. They found no evidence that imperial woodpeckers survive. Only residents in their late 60s or older remembered the bird. Local people said the birds were gone by about 1960, killed by hunting and possibly by poisoning encouraged by logging interests.

In 2011 the team published its analysis in The Auk. The film showed slow climbing strides and a fast wingflap rate compared with other woodpeckers. The authors concluded that human persecution, plus logging of large pines for timber and of dead trees for pulp, were probably the main causes of extinction.

Nobody has questioned the film itself. The caveats are technical. The camera's frame rate is uncertain, and the footage is shaky. The open question is whether the species outlived it. NPR said in December 2011 that the bird was "last credibly spotted in the 1990s." Search for Lost Birds records local claims of sightings from 1965 to 1995. None has been confirmed. IUCN and BirdLife list the species as "Critically Endangered (Possibly Extinct)." The Mexican government has considered it extinct since 2001.

Joel Cracraft of the American Museum of Natural History put it plainly. "It's the last confirmed sighting of an extinct species." Gallagher went on to write Imperial Dreams, published in 2013. Of the film he said: "It's amazing that the bird does so many different things in 85 seconds."