I'd like to "adopt" an endangered species for my daughter's birthday. She'd probably prefer a bear, either polar or panda, since they make the cutest plush toys. But which animal should I sponsor to make the greatest impact?
Your question addresses one of the great controversies in the environmentalist community—conservation triage. Researchers estimate that we're losing as many as 27,000 species every year, about 300 times the pre-human extinction rate. Triage advocates argue that we have no legitimate hope of saving all of the world's endangered creatures, so we ought to think seriously about how to allocate our resources for the greatest effect. Others find this position both defeatist and hopelessly theoretical, and point out that few triage-ists have the courage to recommend specific candidates for extinction. ("Triage is a four-letter word—and I know how to count," says Stuart Pimm, a conservation scientist at Duke University.)
Four factors typically inform triage theory. The first is value. Some species exhibit unique genetic, anatomic, or behavioral traits. If these creatures were to die off, a branch of the evolutionary tree would die with them. Other "valuable" animals have prized economic, cultural, or even aesthetic qualities. (It's apparently OK to talk about cuteness, even among conservationists.)
The second factor is the biodiversity benefit. Conservationists like to protect so-called "keystone" species, on which entire ecosystems rely. Pollinators and coral are classic examples. In other cases, eliminating the threat to an "umbrella species" would help others. For instance, cordoning off a section of the beach to protect a particular nesting bird may also benefit turtles and seals.
Probability of success is the third factor: What are the odds that our efforts will work? It's not always clear what's ailing an animal. We know that a fungus is partly responsible for amphibians' massive, worldwide die-off. But scientists disagree over the reasons for the outbreak. Some think that drugging the frogs may save them. Others think climate change has made them more susceptible to disease, and solving this fungus won't solve the larger problem. Until we can get to the root of the issue, the impact of your charitable giving is uncertain.
In theory, you're supposed to multiply these three factors—species value, biodiversity benefits, and probability of success—and divide the product by the fourth factor: cost. The result should tell you which animal to save.
In practice, however, you'll find it difficult to boil all these factors down into a single ranking. It's easier to focus instead on a few especially good candidates per factor. If you'd like to save a branch of the evolutionary tree, consider the Brothers Island tuatara. While only vulnerable, not endangered, it's one of only two species remaining in its order. Endangered species with unique traits include the Cuban solenodon, one of the few mammals to inject venom through its teeth. If you'd prefer something a little less, well, hideous for your child, consider the culturally, economically, and aesthetically significant Asian elephant. It has profound connections to Hindu traditions and helps villagers work in areas that are inaccessible to machinery. Generally speaking, EDGE (Evolutionarily Distinct and Globally Endangered) is a good organization to support if you're interested in the most unique creatures.
A good resource for high-impact donation strategies is the U.S. Fish and Wildlife Service's Endangered Species Program, which has developed prioritized action lists for endangered species, along with the cost of each action. (Check out example plans for the Florida panther [PDF] or the red wolf [PDF].)You could pick a high-priority, low-cost action item, like protecting habitat or developing a disease prevention plan, then donate your money to the private conservation organization that has partnered with Fish and Wildlife to accomplish it. Your local FWS office can help direct you to the right conservation groups.