Scottish Deer Are Culprits in Bird Killings

James Owen in England
for National Geographic News
August 25, 2003

Red deer on the Scottish island of Rum may be eating the heads and legs of live seabird chicks as a way to get minerals they need to grow their antlers.

Scientists believe this surprising addition to the red deer's diet stems from mineral deficiencies in the vegetation they eat. By munching on Manx shearwater chicks, the deer are able to get the extra calcium they need.

This annual health drive by the red deer of Rum has drawn a National Geographic documentary team to the island. The team hopes to capture the deer's behavior on film for the very first time.

Situated 16 miles (26 kilometers) off the west coast of northern Scotland, Rum has one of the world's largest colonies of Manx shearwaters (Puffinus puffinus). In late August thousands of youngsters start to venture from the safety of their hillside burrows. Still unable to fly, their emergence provides a windfall for predators. And chief among them is that picture of doe-eyed innocence, the red deer (Cervus elaphus).

For years bird-watchers visiting the island nature reserve puzzled over the appearance of decapitated Manx shearwater chicks at the end of each summer. Leg and wing bones were also missing. Everything else, including feathers, flesh and skin, remained intact.

"We find their carcasses up on the hills near the nesting sites," said nature reserve warden Mick Blunt. "The main period of predation occurs when the young ones finally emerge from their burrows. They come out mainly at night for a mosey around. This is when there are rich pickings to be had, especially if there's a full moon and the chicks are clearly visible."

Prime Suspects

While crows, ravens, and eagles sometimes take live birds, Blunt says red deer became the prime suspects a few years ago when a deer hunter saw one chewing a chick.

Blunt added: "I've never witnessed this myself and there's still a lot we don't know about the phenomenon."

Bob Furness, a seabird ecologist at the University of Glasgow in Scotland, is among a handful of scientists worldwide to have researched bird predation by deer. He has also studied bird-eating sheep, on Foula in the Shetland Islands.

His observations revealed that Foula's sheep target unfledged Arctic terns. In years when the island's tern colony was at its largest, more than 200 chicks were found with amputations characteristic of sheep attacks. Ewes were also seen turning over chicks in the nest before biting off their legs.

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