Study reveals the mystery of the ‘lost’ arctic owls that appeared in northern Spain three years ago

In November 2021, three juvenile snowy owls were sighted almost simultaneously in northern Spain. Their extraordinary appearance and beauty (white plumage, black spots and large amber eyes) attracted a large number of ornithologists and curious onlookers. The most common question was how they could have arrived in Cantabria and Asturias from their distant places of origin. Had they escaped from somewhere? Had they crossed the Atlantic perched on a ship? Now a scientific study reveals that they were not born anywhere in Spain or central and southern Europe, but in other Arctic latitudes located in areas of North America, Greenland, Russia, or Fennoscandia (Sweden, Finland and Norway).

“We cannot pinpoint the location, but we have shown that they have not escaped from a zoo or from any cage and that they are not Spanish or European,” explains biologist Carlos Gutiérrez-Expósito, lead author of the research published in the SEO/BirdLife journal Ardeola. It is most likely that they were born in the wild and got lost, as this owl “is a long-distance traveler because the resources of the Arctic are ephemeral and unpredictable, which leads them to move south of their usual range in winter.”

The researchers analyzed the feathers of two of the three specimens that landed in Spain — a male and a female, from whom samples could be taken: the other male disappeared — which, as they were juveniles, had maintained the feathers that grew in the nest where they were born.

“They were kept in a drawer at the University of Cantabria and when I found out about this I thought that an analysis of the heavy isotopes could be carried out,” says the biologist. The aim was to find out what proportion of deuterium (heavy hydrogen) the feathers contained, because “the further north the feather was created, the lower the proportion is, and so we can infer from which latitudes it comes.”

The deuterium content also allowed them to verify that the two specimens analyzed were not siblings and that they were born in different places, which further removes the possibility that they had escaped from somewhere.

What’s more, there are several factors that point to the owls’ wild origins: the exhaustion and weight loss they were experiencing could have been caused by a long journey (probably without food), in addition to the difficulty in adapting to a new environment. This could have caused the immunosuppression observed in the male and the illness in the female. It is also not uncommon for snowy owls to land on ships on the high seas that transport them wherever they go, sometimes to the European coasts. “Therefore, arrival on a ship from North America or Greenland is the most plausible origin of the snowy owls found in northern Spain in 2021,” the study states.

The journey of the birds

The first specimen detected, a male, was found exhausted on November 8, 2021, near the Virgen del Mar beach, in Santander (Cantabria), and died four days later, after being transferred to a recovery center. The second, a female, was sighted in Gozón (Asturias) on November 10. And, three days later, another male was found around three miles away. These last two birds appeared almost 100 miles from the first sighting, the study says. The owls remained in Asturias for several days, “which attracted hundreds of bird watchers, generating the first great rush for a rare species in Spain.” They remained there until November 20, to then be sighted further east: the male in Somo (Cantabria) seven days later and the female 13.5 miles further away, in Santoña (Cantabria) on November 30. “Very close to where the first exhausted male had been found,” the researchers point out.

From there they disappeared, until the male was spotted on the roof of the bullring, near the port of Santoña, almost three months after the first sighting. The crowd appeared again, and remained there until nightfall. The female seemed to be in good health, “showing normal behavior such as grooming and defecating, with her eyes wide open and alert.” But, the next morning, “she was found dead,” the study states. She suffered from advanced aspergillosis, a disease caused by a fungus, which she should have been accustomed to if she had escaped from somewhere nearby.

At the time, most hypotheses pointed to the fact that they were wild specimens that could have arrived on a ship. What strengthened this belief was their simultaneous appearance in coastal areas close to large cargo ports such as Gijón and Santander. In addition, one of the owls had rust on its plumage, something common on the decks of cargo ships. “Based on these facts, the Spanish Rarities Committee accepted the three as wild birds that arrived with the help of a ship,” explains the study. But now, the analysis of stable isotopes offers scientific evidence.

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