"A lot of the time, when people think an animal is abandoned or lost, that's not actually accurate," said Steve Monfort, director of the Smithsonian Conservation Biology Institute. "It's hard if you don't know the full context."
For example, a nest of baby cottontail rabbits may seem abandoned if you can't spot an adult nearby. But mother rabbits spend only minutes a day with their young, and that's a good thing. Unlike their offspring, adult rabbits give off a strong scent that predators can track. If the mother stayed in the burrow, she might inadvertently lure a hungry fox or owl straight to it. She's being the best parent she can be by avoiding her kids entirely.
Another example: Many young birds leave the nest a few days before they're actually able to fly. A fledgling that seems lost and alone to a human observer may just be going through a very normal phase of growing up. Humans who attempt to "rescue" these lost animals often end up doing more harm than good.
The best thing you can do for an animal that appears to be neglected, Monfort said, is call someone from an animal welfare service, rather than try to weigh the costs of interfering with the creature on your own.
If an animal is sick or injured, the calculation is slightly different, but Monfort's recommendation is the same. Sick animals may carry diseases that can infect humans; moving an injured animal may cause further damage. It's always better to let a professional handle it.
There's also a difference between animal rescue and conservation, which you mention in your question. Whether you should help a single injured bird in your backyard is an animal welfare issue. But conservation is about saving species, not individuals. And although individual animals die from natural causes all the time, extinctions are almost always driven by humans.
"The rates of extinction that are occurring are 1,000 times greater in the world than what you would consider to occur by natural processes," Monfort said.
Conservationists will sometimes rescue and rehabilitate sick members of endangered species, particularly if their ailment is linked to human presence — Monfort called that "conservation with a little c." But most of the work of protecting threatened populations is about ensuring that they have the right resources and environment to thrive, despite the incursions of poachers, climate change, deforestation and the like.
Indeed, aiding animals is sometimes antithetical to the notion of conservation. Things like illness, injury and predation can be brutal to witness — but they are also part of the natural system scientists want to preserve. That's why conservationists rarely intervene in individual cases, even when they involve creatures the scientists are trying to protect.
Currently, Monfort is helping with a project to reintroduce the scimitar-horned oryx — a North African antelope that's been extinct in the wild for years — to a nature reserve in Chad. The animals are fitted with radio collars and will be protected from human influence, but "once we reintroduce we more or less let nature take its course," Monfort said.
Don Despain, a retired ecologist at Yellowstone National Park, has said that "the resource is wildness" — a quote that the park now features on its website.
"The importance of Yellowstone is not in preserving five thousand bison, ten thousand hot springs, or three hundred waterfalls," the park explains. "Rather, the park’s significance is in preserving natural ecological processes."
In nature, an injured animal — say, the bird in your back yard with a broken wing — will become food for a predator — perhaps an owl. The remains that the owl doesn't eat will go on to feed microbes that fertilize the soil, which in turn gives rise to new plants, which will feed the insects that become a meal for future birds. This whole system is the "wildness" that Despain speaks of. It's worth thinking about the next time you come across an injured bird.