Gibbon apes, wolves, termites, coyotes, barn owls, beavers, bald eagles, golden eagles, condors, swans, brolga cranes, French angel fish, sandhill cranes, pigeons, prions (a seabird), red-tailed hawks, anglerfish, ospreys, prairie voles (a rodent), and black vultures — these are a few of the creatures that mate for life.
Of course, it depends on what you mean by "mate for life." These creatures do mate for life in the social sense of living together in pairs but they rarely stay strictly faithful. About 90% of the 9,700 bird species pair, mate, and raise chicks together — some returning together to the same nest site year after year. Males, however, often raise other males' offspring unknowingly. DNA testing reveals that the social-pair male did not father 10, 20, and sometimes 40% of the chicks.
Black vultures, though, discourage infidelity. All nearby vultures attack any vulture caught philandering.
Only about 3% of the 4,000 mammal species are monogamous (and Homo sapiens isn't one of them). Beavers, otters, bats, wolves, some foxes, a few hoofed animals, and some primates live together in social pairs but dally sexually much as birds do.
Wolves, for example, are generally monogamous but also breed polygamously if the male is unrelated to the female and prey is plentiful. Moreover, they sometimes have more than one mate in a lifetime, says Dan Stahler, biologist at the
Yellowstone Gray Wolf Restoration Program run by the National Park Service. This happens "if one mate dies, gets kicked out of the pack, or is physically unable to breed due to injury, illness, etc."
Other animals known to mate for life:
Beavers

"You may not realize that beavers are gentle, family-oriented animals who mate for life, raise their children in loving families, and remain lifelong friends with their offspring," writes PETA President Ingrid E. Newkirk. "Not only do these animals epitomize family values, they are also industrious role models: They are master architects whose complex, sturdy lodges last for years, and they constantly maintain their homes, taking obvious pride in their work. Beavers are even known to enjoy flute music."
Seahorses

Seahorses are truly unique, and not just because of their unusual equine shape. Unlike most other fish, they are monogamous and mate for life. Rarer still, they are among the only animal species on Earth in which the male bears the unborn young.
Geese

Geese usually mate for life, though a small number will "divorce" and remate. They tend to lay a smaller number of eggs than ducks but both parents protect the nest and young, which usually results in a higher survival rate for the young geese.
"I'm a farm boy who grew up here in the hills outside Yamhill, Ore., raising sheep for my F.F.A. and 4-H projects. At various times, my family also raised modest numbers of pigs, cattle, goats, chickens and geese, although they were never tightly confined.Our cattle, sheep, chickens and goats certainly had individual personalities, but not such interesting ones that it bothered me that they might end up in a stew. Pigs were more troubling because of their unforgettable characters and obvious intelligence. To this day, when tucking into a pork chop, I always feel as if it is my intellectual equal.
Then there were the geese, the most admirable creatures I've ever met. We raised Chinese white geese, a common breed, and they have distinctive personalities. They mate for life and adhere to family values that would shame most of those who dine on them.
While one of our geese was sitting on her eggs, her gander would go out foraging for food—and if he found some delicacy, he would rush back to give it to his mate. Sometimes I would offer males a dish of corn to fatten them up—but it was impossible, for they would take it all home to their true loves.
Once a month or so, we would slaughter the geese. When I was 10 years old, my job was to lock the geese in the barn and then rush and grab one. Then I would take it out and hold it by its wings on the chopping block while my Dad or someone else swung the ax.
The 150 geese knew that something dreadful was happening and would cower in a far corner of the barn, and run away in terror as I approached. Then I would grab one and carry it away as it screeched and struggled in my arms.
Very often, one goose would bravely step away from the panicked flock and walk tremulously toward me. It would be the mate of the one I had caught, male or female, and it would step right up to me, protesting pitifully. It would be frightened out of its wits, but still determined to stand with and comfort its lover."
Taken from "A Farm Boy Reflects"The New York Times, July 31, 2008
By Nicholas Kristof