This year, one of the giraffes at the North Carolina Zoo turned 32 years old, making it the second oldest giraffe in captivity in the world. In March, the zoo's oldest chimpanzee turned 40 -- not ancient in terms of life expectancy for chimpanzees but certainly past its prime of life.

These two species illustrate a growing concern for zoos in America and throughout the world: captive animals are living longer, and their extended care into old age has become a growing concern for most zoos and other institutions housing animals.

Animal welfare groups likely would say that it's good that animals are living longer in zoos and facilities. It illustrates how zoos are doing their job well. But it also means zoos must now deal with increasingly difficult aging problems.

Animals that would have long before died in the wild are now developing such ailments as cancer, renal failure, and heart and liver disease.

"The problems that we see in older animals are similar to those we see in older people," said Dr. Mike Loomis, chief veterinarian at the N.C. Zoo. "We start seeing degenerative processes. For instance, we have several animals that have joint problems; we have animals that develop tumors as they age -- just like humans."

Like humans, animals are living longer because of improved nutrition, better veterinary care and medical breakthroughs. Also, as they age, animals in the wild usually die off naturally or are killed by other animals. But in zoos, they have no predators, so they live longer.

The easiest approach to the aging problem in zoos would be simply for them to euthanize aging animals once they become too old to be exhibited, but as long as their quality of life is good, zoos have a moral obligation to care for their aging animals. And like most accredited institutions housing animals, the N.C. Zoo makes a commitment to a particular animal from the time it arrives at the park until the time it leaves for another institution or dies naturally.

"As the animals age out, we honor that commitment to them," Loomis said.

"We do our best to provide them adequate care during the prime of their life, and then as they age, we continue to provide them the best possible care."

Although zoos could simply move the aging animals off exhibit, it is often necessary to maintain diversity in the ages of animal collections. Younger animals are typically more active and are of more interest to visitors, but older animals are necessary, too, particularly in species that develop social groups.

The older animals are, in a sense, role models for younger animals, teaching them proper behavior within their social groups.

This aging in captive collections has created the need for zookeepers to learn how to accommodate these aging populations. Although zoos have always faced the problems of aging animals, today it has become an evolving part of their animal husbandry -- learning how to care for older animals and to meet their needs.

Similar to human populations, it's not that zoos have never dealt with aging animals; it's that aging animals are now in greater numbers proportionally.

Often zoo animals, just like household pets, grow weak with age but are not old or sick enough to be euthanized. Suffering from typical aging maladies such as hearing and sight loss, cancer and dementia, zoo animals often have to be treated with expensive painkillers and other medications. Often, zoos simply have not budgeted for these higher, long-term health-care costs.

Adding to the aging dilemma are the emotional complexities brought on when both visitors and keepers grow to love the institution's animals over the years and decades. And, as with companion pets, the choice to finally euthanize a zoo animal can be difficult and emotional.

Simply put, zoos and other animal institutions are responsible for the well-being of their animals for as long as those animals live -- no matter how long that might be. But the new problems facing zoo staffs are taking them -- and the animals -- into an area of limited experience and many unknowns.

Tom Gillespie works for the public affairs office at the N.C. Zoo.