The article, Audubon’s Bird of Washington: unravelling the fraud that launched The birds of America, makes an impressive case.
The author, Matthew R. Halley of the Academy of Natural Sciences of Drexel University, Dept. of Biodiversity, Earth & Environmental Science, at Drexel University, conducted an exhaustive search for primary (non-print) sources in multiple archives in the USA and transcripts in the literature.
Halley, believes his research demonstrates “beyond reasonable doubt that Audubon’s painting of the Bird of Washington was  was the product of both plagiarism and invention.”
“The preponderance of evidence suggests that the Bird of Washington was an elaborate lie.” Halley concludes, “that Audubon concocted to convince members of the English nobility who were sympathetic to American affairs, to subscribe to and promote his work.”
“Audubon never produced a specimen with the anatomical characters of the Bird of Washington, as shown in Plate 11.”
In 1996 Partridge noticed a striking resemblance between Audubon’s painting of the Bird of Washington and an older image labelled ‘Golden Eagle’, ostensibly depicting Aquila chrysaetos (Linnaeus, 1758), published in an edited serial work The Cyclopædia.
Evidence points to the published plate [from The Cyclopædia] as [Audubon’s] direct source. The golden eagle is perched on its out-cropping precisely as is Audubon’s bird, with other similarities between the two paintings.
Audubon had access to The Cyclopædia during his residency in Cincinnati, just prior to the date on his Bird of Washington painting.
After nearly two centuries, the species is still known only from Audubon’s anecdotes and plate, and secondary sightings by his friends.
The article also makes an impressive case that Audubon plagiarized other painting to create images for The Birds of America.