PORTLAND, Ore. -- The Oregon Zoo is down to a lone gray wolf.

Veterinarians recently euthanized Ceann following surgery to remove a tumor from her shoulder. Her death leaves Marcus as the last member of the pack.

The life expectancy of a gray wolf is six to eight years, but those in captivity often live longer. Zoo veterinarian Mitch Finnegan said Tuesday that Marcus just turned 13 and medical problems hamper his mobility.

Ceann and Marcus were born in April 1995 in Battle Ground, Ind. They arrived at the Oregon Zoo two months later.