Zoos are like fancy hotels, albeit without the fluffy pillows and individually packaged soaps, or so says Daniel Frynta, an ecologist at Charles University in Prague. Only the "richest" animals get to check in. And if an endangered species gets a room, he says, it might just survive.

Frynta defines a rich animal as one that we humans find appealing. And, he says, we have very specific taste: It's got to be big. It's got to be cute. It's got to behave or look humanlike. If a critter is colorful, we like it. We also like it when zoo denizens play and speak and travel in family groups. Those animals, he says, get to stay in zoos. "Poor" animals—that is ugly ones—stay outside where their habitats are quickly being destroyed.

Species in zoos are often protected from total extinction because they are commonly the subjects of captive breeding programs in which staffers entice animals to mate and reproduce offspring that can then be released into the wild or shared with other zoos. Although it's hit or miss, captive breeding represents the last hope for survival for many species. The Hawaiian crow and the Seychelles giant tortoise only exist in zoos, for example. The Arabian oryx was once extinct in the wild, but captive breeding programs allowed for the release of individuals back into their native habitat. And zoos often fund conservation programs that happen outside their walls.  "The record is imperfect," says Nate Flessness, science director at the International Species Information System, "but zoos are the only ones doing anything."

David Stokes, an ecologist at the University of Washington Bothell, agrees, noting that a biodiversity crisis is at hand. The current rate of extinction is up to 1,000 times faster than it would be without humans, according to the International Union for Conservation of Nature and Natural Resources (IUCN). The surviving species will "be the ones we decide to save," Stokes says. If zoos decide not to save "ugly" animals, they could go extinct. Snails and insects, for example, almost never make it into zoos.

The ugly truth: Zoos are businesses
Still, zoos have their drawbacks: Studies comparing the life spans of animals in zoological parks with their wild counterparts have found that captive animals tend to live shorter lives. Elephants, for example, live an average of 36 years in the wild, but only 17 in zoos. For many species, however, zoos can be a vital refuge from poaching, habitat loss and disease.

Yet, Frynta's research shows that zoos may not be entirely living up to their conservation promises. In a September 7 PLoS ONE paper his team asked Czech citizens to rank pictures of endangered and non-endangered parrots from most to least beautiful. The researchers then compared the rankings with worldwide zoo holdings and species' conservation needs as defined by the IUCN. Overwhelmingly, zoos are keeping pretty birds rather than endangered ones.

That's because zoos have another kind of survival to worry about—their own. "We have to deliver what our visitors want," says Greg Bockheim, director of the Virginia Zoo in Norfolk. Visitors want to see animals they like and recognize. Frynta agrees: "Zoos full of endangered but ugly animals will never make money."

And although gorillas and lions would not have to empty their bank accounts—if they had them—to check in at these so-called hotels, such popular mammals can certainly entice visitors to empty their own pockets. A white tiger, Bockheim says, can triple zoo attendance—And directors could put that money toward conservation for less beloved animals, he says.

Many zoos, however, are reluctant to discuss their efforts to balance conservation priorities and profit. Calls to more than a dozen zoological organizations were not returned, including the Wildlife Conservation Society, a conservation organization that also manages five zoos in the New York City area.

Universal animal aesthetics
A solution may lie in the fact that unlike ideas about human beauty, our love for some animals and ambivalence toward others may beuniversal, Frynta says. In a cross-cultural study comparing students in Prague with tribespeople in Papua New Guinea, Frynta's team found that the two groups think the very same snake species are beautiful.

By knowing what people do like, zoos could enhance the public's support of species we don't want to cuddle with, Frynta says. Want the public to connect with a snail or a bat? Give it a human name, like George or Sally; tell people about its family; design an exhibit that allows visitors to understand the animal's daily life, Bockheim says.

And, if directors can't get everyone to love a homely beastie, pick a prettier but still threatened one. In every group of animals, Frynta says, "we can find some species which are highly preferred and also endangered." By protecting the panda, zoos can encourage the conservation of the entire forest in which it lives—including the charismatically challenged animals that also call it home.

Others are less optimistic about the fate of creatures that have a dearth of animal magnetism. "Of course they are doomed. Why wouldn't they be doomed?" asks Anna Gunnthorsdottir, an economist at the University of New South Wales Australian School of Business in Sydney who studies how human preference changes conservation behavior. Even if zoos follow all of Bockheim's suggestions, there are just some animals we may never love.

Last year, for example, the United Nations Convention on Migratory Species declared 2011–12 the Year of the Bat. Their Web site does all the things Bockheim suggested; it says bats are "exceptional, delightful, fascinating and likeable." The Year of the Bat follows the Year of Biodiversity, the Year of the Gorilla, and the Year of the Frog, each of which the World Association of Zoos and Aquariums (WAZA) celebrated with activities at zoos all over the world. This year, however, they will not be planning anything big. Bats are simply "not a topic that will attract that much attention," says Markus Gusset, WAZA conservation officer.

And even if zoos wanted to breed every endangered species in the world, there just isn't room in zoos, Bockheim says. "You can't save everything, that's just how it is."

Frynta, however, is not ready to give up just yet. He has faith in the conservation community. "We have just one goal," he says, "the survival of endangered species." And their survival, he adds, may have little to do with the animals themselves. It could simply depend on how we manage our guest list.

This article is provided by Scienceline, a project of New York University's Science, Health and Environmental Reporting Program.