What are barnacle geese and how do they grow? Well, before the migration patterns of birds were known there were some strange ideas about the origin of geese.

From Branch to Goose

Birds might appear to not exist for months at a time, and scholars had some creative theories as to why. They observed that goose barnacles on driftwood greatly resembled a certain type of goose. Clearly geese weren’t always visible because… they were busy growing on wood!

Logically, if Barnacle Geese grew like a fruit or vegetable, than they must be a fruit or vegetable. Medieval monks tended to follow culinary restrictions, and this revelation made meatless days far less painful. Barnacle geese were also quite abundant in medieval Europe. This gave clergy an additional reason to want to believe in their plant-based origin.

“…I … heard that in Scotland there was once a tree growing on the bank of a river which produced fruits shaped like ducks. When these were nearly ripe, they dropped down of their own accord, some onto the earth, and some into the water. Those that landed on the earth rotted away, but those that sank into the water instantly came to life, swam out from below the water, and immediately flew into the air, equipped with feathers and wings.“

Aeneas Silvius Bartholomeus (1435)

Critics of the Fruit-Birds

However, there were critics of the claim that this was in fact guilt-free eating. In 1215, Pope Innocent III made a point to prohibit their consumption during Lent. His argument was that despite their strange method of reproduction they lived like ducks and must be of a similar nature.

“…Bishops and religious men (viri religiosi) in some parts of Ireland do not scruple to dine off these birds at the time of fasting, because they are not flesh nor born of flesh… But in so doing they are led into sin. For if anyone were to eat of the leg of our first parent (Adam) although he was not born of flesh, that person could not be adjudged innocent of eating meat.”

Giraldus Cambrensis (1188)

We can’t help but see this logical conclusion as a skit right out of Monty Python’s Holy Grail. “Who are you who is so wise in the ways of science?” Still, it is very fortunate for us that barnacle geese superficially resembled goose barnacles. Medieval illustrators have provided us fascinating drawings to examine.

Barnacle Geese in Print

The below left image comes from Ornithologiae (1603) by Ulisse Aldrovandi (1522-1605) an Italian naturalist. He has been described as the father of natural history studies by notable naturalists. The list includes Carl Linnaeus, who formalized binomial nomenclature, the modern system of naming organisms. Aldrovandi’s accomplishments lie in many directions. He authored hundreds of books and essays, amassed an enormous cabinet of curiosities, created a botanic garden in Bologna (now known as Orto Botanico dell’Università di Bologna), and even invented the word “geology”. If you enjoyed the images of barnacle geese and are interested in viewing other oddities, there’s plenty more out there. We recommend starting with Aldrovandi’s Monstrorum Historia published after his death in 1642.

This below right image is from The Herball by John Gerard (1545 – 1612) from an edition published after his death in 1636. Gerard was an English botanist, and The Herball was the most widely read English botany book in the 17th century. It famously contains the first English description of the potato. It consists of over 1800 woodblock images reused from other authors’ publications (and often mislabeled) alongside 16 original etchings. Gerard’s biography is a worthy read if you’re interested in authorship, piracy or appropriation.