Of the 4,000 or so species of mammals, only a handful of animals have ever been thought to mate for life. This short list of animals includes among others: gibbon apes, wolves, coyotes, barn owls, bald eagles, gorillas and barn swallows.

But as it turns out there are some cracks in these monogamous images — and whether these creatures’ faithful reputations hold up or not comes down to how one defines “mate for life.”

Animals may be socially monogamous, staying together in pairs for anywhere from a lifetime to just a season, but that doesn’t mean that they don’t have cheating hearts. And, according to Kevin McGraw, an Arizona State University life sciences professor who specializes in mating systems and rituals, only 3 to 10 percent of mammals are even socially monogamous.

Wolf alpha pairs are usually monogamous with each other, but alpha males have been known to stray with other pack members, especially if they are closely related. Among red foxes, long considered extremely loyal, mate switching has also been shown. DNA fingerprinting in one study proved that 80 percent of red fox cubs were the product of extracurricular activity by females.

The reason why some animals live in exclusive pairs and still engage in flings on the side seems to be related to parental care. Foxes, for instance — like barn swallows and more than 90 percent of all bird species — form lasting pair bonds with their mates. These bonds allow both parents to care for the young — a practical way to deal with the demands of child rearing.

More than 90 percent of bird species form lasting pair bonds with their mates.

Sexual monogamy, where animals have only one mate forever, is rare because evolution favors promiscuity. Some females of a species may choose to live with a mate who is a good provider, but they may keep looking for other males, who have “better” genes that will produce better offspring. Also, in the animal kingdom it may pay to sleep around, because relying on a single mate is risky business.

“If one’s mate were to be harmed, to disappear, or to lose their life, an animal’s reproductive success would suffer permanently were it not to find an alternate mate,” said McGraw. “By increasing their number of mates, animals should generally produce more and better young.”

Perhaps, monogamy’s only true success story lives in the intestines of fish — where a flatworm physically attaches itself to a mate for life, according to an article in The New York Times.

“There may be other animals that are truly monogamous, but the data is not out there. It’s a matter of cautious science,” McGraw explained.

While social monogamy is very rarely accompanied by sexual monogamy, there are plenty of animals in which males and females share mutual affection and exhibit a certain amount of fidelity.

While it may not be “till death do us part” in the strictest sense, faithfulness has its advantages and it will have a place in the animal kingdom for a long time to come.

Each January, the people of Kundha Kulam, a parched farm town in southern India, raise their eyes to the sky, searching for signs of life-giving rain. But they are not looking for clouds. They are watching instead for the birds that arrive on the vanguard winds of the oncoming monsoon. At the sight of the first flick of feather, the villagers breathe a sigh of relief, knowing that their crops will soon get a welcome drink.

This week, NATURE takes you from Kundha Kulam’s vibrant monsoon marshes to the rugged American Rockies to explore the worlds of Extraordinary Birds. Along the way, viewers meet a Scottish father and son who have taken up the ancient hunting art of falconry, a performer who works wonders with a pretty smart parrot, and some senior citizens who have developed strong attachments to some feathered friends. There are also homing pigeons that deliver film, rat-catching barn owls that protect farmers from pests, and hummingbirds that show their prowess as long-distance flyers.

In each case, NATURE’s Extraordinary Birds highlights the intimate links that people have forged with birds. In Kundha Kulam, for instance, “if the birds come, we know we will be prosperous,” says a resident. Like the robin that is the harbinger of spring, or the lonely honk of a migrating goose that signals the arrival of another winter, the herons, ducks, and pelicans that swarm to the flooded fields around Kundha Kulam have become a powerful symbol of the cycle of life.

In many instances, however, birds are more than just symbols — they are companions. In a convent in New York state, for example, Sister Barbara Seaward has founded the group Feathered Friends. She, along with others in her community, conduct pet therapy sessions for those in nursing and retirement homes. The residents agree that there is nothing quite like a visit from a cockateil or a cockatoo to lift the spirits.

And in the whitewater rafting canyons of Colorado, guides use homing pigeons to safely deliver a valuable commodity — photos of customers splashing their way down the rapids — back to home base, so the keepsakes are waiting when the rafters return from their adventure. The flying film couriers have become an essential business partner.

In eastern India, homing pigeons play a different role: they are law enforcers. Despite the introduction of radios and e-mail, the state police force of Orissa still keeps nearly 700 pigeon police available to shuttle messages between far-flung stations, according to British Broadcasting Corporation reports. But the century-old pigeon force may not last long into the millennium, as budget makers are convinced the birds are no longer needed.

In Florida, however, sugar cane farmers are eager to enlist the aid of birds. With help from University of Florida researcher Richard Raid, who is featured on NATURE’s Extraordinary Birds, the farmers have encouraged ghostly-white barn owls to nest near their fields. The birds perform a valuable pest control service, with each nesting pair capable of catching and eating almost 3,000 rats a year. They are “nature’s rat traps,” Raid says. Each year, the rodents cost sugar cane farmers nearly $30 million in crop damage.

Like other birds, however, the barn owl is a powerful symbol for many. “Many people in the [Caribbean] islands and Central and South America believe that it is bad luck to see a barn owl, particularly during the day,” says Raid. “Rumor has it that to see one forewarns the death of a friend or a relative in the very near future.”

Despite their scary reputation, however, the once common owls are becoming endangered in some areas and need some human help, such as the construction of nesting and roosting boxes. Raid and his colleagues are testing models of barn owl boxes mounted on posts to see how receptive the birds are to such homes. Sugar cane grower Wayne Boynton, who has earned the nickname “Godfather of Barn Owls,” says owls have moved into all the boxes he has put up on his 3,000-acre farm. “It’s like [the movie] Field of Dreams,” he says. “If you build it, they will come. It’s that simple.”

Echoing a sentiment heard elsewhere around the world about other birds, Boynton believes that “you can’t have too many barn owls.” They are, indeed, extraordinary allies.

Intrepid avian creatures attain new heights in NATURE’s Extraordinary Birds.

The gift of flight would seem reason enough for humanity’s fascination with birds. But there’s even more to it than that. Birds are remarkable for a wide range of exceptional physical abilities, for their indications of intelligence, and — for some species — their surprising level of rapport with humans.

In the small Indian village of Kundha Kulam, for example, birds’ arrival are a sign to the townspeople that rain will follow and that their crops would soon thrive. While falconry — the art of training hawks, falcons and other birds of prey to hunt — exemplifies the partnership men and birds can develop.

Humans have also relied on the more prosaic pigeon. Although city dwellers may dismiss them as flying rats, no bird can top the pigeon for courage and service to humankind. Since pigeons have the ability to find their way “home,” many were used in dangerous, top-secret missions in World War I and II, delivering important messages to Allied troops behind enemy lines.

Discover more amazing birds — from hummingbirds and peregrine falcons to parrots and barn owls — on NATURE’s Extraordinary Birds.

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Online content for Extraordinary Birds was orginally posted November 2000.