World Osprey Week: The Osprey

The 22nd–26th March 2026 is World Osprey Week. To mark this, as well as the 350th anniversary of the year of the publication of Francis Willughby’s Ornithologia, this post will focus on part of the description of the Osprey provided in Ornithologia.

The Osprey is particularly problematic in Ornithologia. The size and other characteristics of the Osprey caused significant problems for Willughby, Ray and other later naturalists because it was an intermediate species that did not fit general classification categories. Historically, the principal distinction between eagles and hawks was their size, but the Osprey sat between the two. Therefore, in Ornithologia, the Osprey was actually entered under two names, Osprey in the eagle category and Bald Buzzard in the hawk category. The description provided under the Bald Buzzard was accurate for the modern description of the Osprey. The classification conundrum was solved in 1809 when it was classified in its own family of Pandionidae.

The "Bald Buzzard" in Francis Willughby's Ornithologia

The bird of this species that they measured weighed 56½ ounces (about 1.6kg). Ray openly questioned Willughby’s measurement in the text because that weight would enable it to pass for an eagle. However, this is within the correct weight range for an adult Osprey, especially for a larger heavier female. Its wingspan was 60 inches (about 1.52m), which is also correct for this species.

The beak from the point to the angles of the mouth was 1½ inches long (3.81cm). It was black, hooked, and covered from the base as far as the nostrils with a blueish cere. The irises of eyes were yellow and the pupils were large. The eyes were not as withdrawn under prominent brows as in the Common Buzzard.

In colour, the upper part of the bird was black and ferruginous. The feathers on the crown of the head were white, which was why it was given the name Bald Buzzard. The throat, breast and belly were white, but the feathers were ferruginous above the crop. The legs were clothed with white and soft feathers. There were about 28 feathers in each wing. From the seventeenth feather, they ended in sharper points and the largest feathers were blacker. In the four outermost feathers, the lower half of their interior vanes were twice as broad as the upper. All of the interior vanes were variegated white and black alternately, indented like the teeth of a saw. The feathers under the shoulders were white, marked with black spots toward the tips. The third and fourth row of those that covered the roots of the flight feathers were elegantly marked toward the tips with dusky spots underneath and had ferruginous edges. The lesser feathers above those were white, the larger feathers beneath them a dusky or brown colour. The tail was made up of 12 feathers of equal length and they were indented as in the wings. The borders of these feathers were white and ferruginous particoloured.

The legs were long. The feet were thick and strong and of a pale blue or verdigris colour. All the toes were armed with great, semi-circular, black, round talons. The feet were scaly and uneven. The sole of the foot was rough so that it may more easily hold its prey after catching it. The toes were disposed so that the outermost of the fore toes could turn backwards, as in owls and parrots.

Osprey, 2010. Yathin S Krishnappa, CC-BY-SA 3.0, via Wikimedia Commons.

It haunted rivers, lakes, and great pools of water, as well as the seashore. It preyed upon fish, which seemed very strange and wonderful to them because it was neither whole-footed nor provided with long legs or a long neck. At Penzance in Cornwall, they saw one that had been shot, still holding a mullet in its claw.

In Ornithologia, it was stated that this bird gave off an unpleasant strong scent. What is known today is that this “Oil of Osprey” was a pungent waterproofing oil produced by a uropygial gland located at the base of an Osprey’s tail. Because the Osprey dives underwater, they produce a much heavier and more potent oil than other raptor birds in order to keep their feathers water-resistant.

Willughby and Ray debunked what they called a “fabulous” tale about this Oil of Osprey. The tale said that this oil was present in the rump of the bird and, when she hung in the air, she let the oil fall drop by drop into the water. This oil then stupefied the fish and they were thus unable to resist being taken by the Osprey. They also noted that some fishermen were so vain as to have claimed to have used Oil of Osprey on their receipts for catching fish. They also debunked the long-held claim that the Osprey had one webbed foot and one clawed.

Further Reading: John Ray, Francis Willughby's Ornithologia, 1678, pp.59, 69, T1, T6.

Author - Debbie Jordan, Middleton Hall Volunteer.

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