ANCHORAGE (AP) -- Zookeeper Todd Byard bangs on the roof of Morning's den and the arctic tundra wolf crawls out of her cozy home.
''She does have a really nice coat,'' said zoo curator Pat Lampi.
Morning is 17 years old. One of the zoo's Siberian tigers, Martha, is 20 years old.
''Some days you worry about her,'' Byard said of Morning. ''Then the next day she's fine... bouncing around and full of energy.''
Morning is old for a wolf. She stood, stretched and sometimes swayed back and forth, a sign of age. She gets medication, like other zoo animals, and is probably the oldest or one of the oldest wolves in captivity, according to one of Byard's wolf books.
While Morning's coat is healthy, her hips and rear end are stiff and sore.
''She still likes to play with the ravens,'' Byard said. ''The ravens pull her tail sometimes.''
Martha and Morning; a 15-year-old sandhill crane named Sandy; a 12-year-old silver fox named Foxy; and Aurora, a 16-year-old red-tailed hawk, are old. Jake, the zoo's black bear, will be 19 next spring. He could live for another six years.
''You have to feel good when the animals'' live long and healthy lives, Lampi said. ''We rely on the keepers to know how they walk and act and eat.''
Watching the animals age is tough, Byard and Lampi said. A musk ox named Tess, known for being the feistiest musk ox at the zoo, was euthanized. She lived more than 20 years. Musk oxen usually die at 15.
''That's the hard decision here to make,'' Lampi said as he looked at Tess' file. ''She was getting thin. Her coat didn't grow like it had in the past. It was the most humane thing to do.''
When Binky and Nuka, two famous polar bears, died in 1995, people visited their empty pen and left bouquets of flowers. When Annabelle, a beloved Asian elephant, died in 1997, people called to offer condolences.
But as older animals die, new ones arrive.
Martha the Siberian tiger and her two male offspring, Al and Steve, arrived in 1995. Martha was named after George Washington's wife because she was born on the Fourth of July, Lampi said.
''She has outlived all of her siblings,'' he said.
Because of her age, Martha gets whatever she wants, said zookeeper Thomas ''Smitty'' Smith. Siberian tigers usually live 15 to 20 years in zoos, he said. One tiger, at the San Diego Wildlife Park, lived to be 26, he said.
''She could go on to 21 or 22 easily,'' Smith said, looking at Martha through the bars of her cage.
In the past few years, she's lost weight. Her voice is a little raspy, and like older large cats, she is prone to urinary problems. She also can't tear into big slabs of meat because she's had dental work.
''She's not senile,'' Smith said as he slid Martha's medication into her morning serving of raw meat. ''She's very aware of who I am and who the boys (Al and Steve) are.''
When Martha dies, she probably won't be replaced, Lampi said. There are strict regulations regarding Siberian tigers. When Morning dies, she will be replaced. The zoo plans to expand her pen and hopes to get more wolves.
The area Binky and Nuka lived in is being remodeled with the hope that the zoo can obtain snow leopards, Lampi said.
''You have to be careful, . . . you have to let go,'' Smith said as he worked with the tigers. ''Animals very rarely live as long as humans.''
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