The cause of death for a snowy owl blown to the Island last year is still unknown after an inconclusive autopsy.

Conservationist David Wingate said he had suspected the bird may have been killed by secondary poisoning — eating a rat which had itself eaten poison. While he said that was still a possibility, the bird didn’t exhibit the typical symptoms.

“There was no internal bleeding, which you usually see when an owl consumes an anticoagulant poison, which we have seen in the barn owls,” he said. “It did have a very green spleen but what the cause of that was we don’t know.”

He said the bird also had a prickly pear thorn lodged in one of its talons, an injury likely suffered while hunting rats, but the injury did not appear to be infected and the bird otherwise seemed in good health.

“It was a immature male bird and it was definitely not starving. In fact, quite the opposite,” Dr Wingate said.

“All we can say is it seemed like a relatively healthy bird that got very sick for an unknown reason and just fell off its perch.

“It certainly looked that way on the day before it died. Its wings were dropped very dramatically. We misinterpreted it as the bird was absorbing the sun, but in retrospect it must have been in the process of dying.”

He said a number of snowy owls have been spotted further south than usual, a phenomenon being attributed to a overabundance of food in their usual habitat.

“The consensus is that the eruption this year was due to an excess of lemmings, so the owls have a big brood with most of the brood surviving,” he said. “Then there are too many in a territory so they chase them away.”