Scientists at the Natural History Museum, UK, have discovered that a strange knob-like ball on the wings of an extinct bird species called the Rodrigues Solitaire was a deadly weapon, used by the bird to defend territory and its mate.

The Rodrigues Solitaire (Pezophaps solitaria) was a giant flightless pigeon that, like its closest relative the dodo (Raphus cucullatus), became extinct soon after European explorers settled in its habitat. It had a knob-like ball on its wings and although it was known to be aggressive, it was unclear what this structure was for, until now.

Dr Julian Hume and Dr Lorna Steel studied records from the 18th and 19th centuries, when many detailed studies were written by Europeans explorers in Rodrigues, on the Mascarene Islands in the Indian Ocean. They also analyzed in microscopic detail the ball structures on fossil solitaire bones.

They found that the so called ‘musket ball’ was indeed a weapon and that it was not found in any other bird. The largest they uncovered grew to 1.3 inches (3.3 cm), nearly as large as a ping-pong ball.

Both sexes had musket balls, but it was only the larger adult males, which grew to about the size of a goose, that had the largest growths, and they seemed to only occur once the bird had obtained a breeding territory and a mate to defend. The findings appear online in the Biological Journal of the Linnean Society.

“The musket ball in the wing looked just like the lead balls that were fired out of an 18th century musket, which is why the early travelers to Rodrigues gave it that name,” Dr Steel said.

“In life, the musket ball would have been covered by a hard skin, almost like a boxing glove, which would have made it very much larger and more lethal,” Dr Hume added.

“There were even reports that it made a sound like thunder. To swing this large, heavy weapon so fast that it made a noise like thunder, it would have needed strong wing musculature. So it becomes clearly apparent why the Rodrigues Solitaire had a large keel on the sternum for the attachment of the wing muscles compared with that of the dodo. Also it explains why so many bones were fractured during fights.”

Some other bird species today have a similar knob-like structure or a different type of weapon in the wing, such as a spike, but there is nothing exactly like the musket ball of the Rodrigues Solitaire.

It’s estimated that there are around 5,000 solitaire fossils in collections around the world. However, there are only 7 almost complete skeletons, the most recent discovered by Dr Steel in Caverne L’Affouche on Rodrigues in May, 2013.

“Getting a true picture of what the bird looked like in life is still a bit of a challenge as there is no bird species left on Earth that is comparable. Very fortunately, there is a drawing of the bird, the only one known, which gives a good idea of what the Rodrigues Solitaire looked like in life,” Dr Hume said.

“As the Rodrigues Solitaire was the closest relative of the dodo, a bird we know practically nothing about, this research has also given a better understanding of the behavior in these birds, especially the dodo of which.”

“We can now say with some authority that the dodo was sexually dimorphic (different size in the sexes), but much less so than the Rodrigues Solitaire, was territorial, and defended its territory with its beak (and not with its wings as did the solitaire).”

______

Bibliographic information: Julian P. Hume & Lorna Steel. Fight club: a unique weapon in the wing of the solitaire, Pezophaps solitaria (Aves: Columbidae), an extinct flightless bird from Rodrigues, Mascarene Islands. Biological Journal of the Linnean Society, published online May 20, 2013; doi: 10.1111/bij.12087