His mission: To collar giraffes and collect tissue samples from the animals, which have been rapidly disappearing from Africa in what Fennessy calls a "silent extinction." (Related: "Giraffes, Zebras Face Surprising Top Threat: Hunting.")
After successfully handling one of the Gambella giraffes, Fennessy and his team headed out again in search of another. But as they flew over the park, they spotted cattle—and herders armed with AK-47s.
"They aimed their weapons at us," Fennessy recalls, "and started firing. And they hit us." The pilot swooped away, evading most of the bullets, and landed to inspect the damage.
"It was minimal, so we continued on and checked on the giraffe we'd collared the day before. He was only two kilometers [1.2 miles] away from the people"—and their guns.
The attackers, likely part of a South Sudanese militia returning from a livestock raid in Ethiopia, did not harm the animal. Some militia groups and local people in Ethiopia hunt giraffes for food and their tail hair, which is used for ornaments.
The incident shows how studying giraffes has become a sometimes risky task, says Fennessy, executive director of the Namibia-based Giraffe Conservation Foundation (GCF).
And an urgent one. Over the past 15 years, numbers of the world's tallest animal have plummeted from an estimated 140,000 to a low of about 80,000. That's a shockingly precipitous drop from the possibly more than 2 million animals that roamed the continent 150 years ago, according to GCF.
Though any schoolchild will tell you what a giraffe looks like, most people don't know about the animals' plight.
The giants strike many as so gentle and unobtrusive—quietly grazing on treetops, bending down to touch noses with a newborn—that discovering that they too, like most of the world's megafauna, are headed toward extinction is like a blow to the gut.
Like many other creatures the world over, the long-necked herbivores have declined mostly due to habitat loss and threats from the growing human population, such as poaching.
In northern Tanzania some people kill giraffes for meat by hanging neck snares in trees, which suffocate their victims. In other parts of Africa, giraffes step into snare traps that have been set for other animals and die from an ensuing infection.
"Giraffe face the same problems that other wildlife species do. It's just that they've been overlooked," Fennessy says.
That's because many conservation groups are focused on protecting other endangered African species, such as elephants, rhinoceroses, chimpanzees, and gorillas.
Efforts to help giraffes, which roam throughout sub-Saharan Africa, are complicated by a lack of scientific knowledge. For instance, some experts still don't agree how many species there are.
Science now recognizes only one species, Giraffa camelopardalis—listed by the International Union for Conservation of Nature as a species of least concern—and nine subspecies.
Only two of these subspecies, the Nigerian and Rothschild giraffes, are considered endangered, but Fennessy fears that others may be as well. Giraffes in Gambela National Park, for instance, are thought to belong to the Nubian subspecies, but no one actually knows.
You have to know what you've got before you can save it, so "we're starting with the basics," says Fennessy.
"How many giraffes are there? Where are they? How far do they range? And how many species and subspecies are there?"
Once biologists sort out the species question—perhaps by sampling the DNA of wild giraffes—conservationists can determine which ones are actually rare and in need of protection.
Already, in response to the dramatic decline of giraffes, park authorities and several African countries have begun taking action.
The week before the shooting incident, the African Parks Network and the Ethiopian Wildlife Conservation Authority surveyed Gambella National Park and counted between 100 and 120 giraffes—the first time the animals had ever been tallied.
The low number suggests that this population could easily blink out unless it's actively protected.
"That's the total for all of western Ethiopia, which covers about 30,000 square kilometers [11,500 square miles]," Fennessy says. "There should be more, and the park wants to help make that happen."
The first step is tracking those collared giraffes to find out where and how far they roam. If the animals regularly travel into areas where they're likely to encounter humans, the park's rangers may need to begin active patrols.
Such protective policies have brought the West African giraffe (G.c. peralta) back from a dangerous low of 50 animals in the mid-1990s to around 200 today. This subspecies lives only in Niger; none live in captivity.
"If we lose this population, then this subspecies—which may actually be a separate species—is gone forever," Fennessy says.
Niger's efforts have also bolstered tourism: Visitors can walk within 50 feet (15 meters) of these giraffes without frightening them, something that's impossible in Tanzania and other countries where the animals are hunted.
In northern Kenya, conservationists are working with local Samburu communities to save a subspecies called the reticulated giraffe. (Read about the elephants of Samburu in National Geographic magazine.)
"Reticulated giraffe are primarily found in pastoralist lands," says David O'Connor, a conservation ecologist with San Diego Zoo Global, which is involved in the project.
The Northern Rangelands Trust, a group of northern Kenyan community conservancies, collects data from rangers who survey wildlife on the ground. Those data show that the distribution of reticulated giraffes has stabilized over the past four years in the region, with a slight increase in sightings in 2013.
John Doherty, project coordinator for the Reticulated Giraffe Project, notes by email that since the Northern Rangelands Trust data is based on giraffe sightings, "they provide an indication of distribution, but not of abundance."
"The surveys cannot, therefore, be used to reliably assess changes in population size."
In August, O'Connor and team will begin surveying the Samburu about their beliefs and attitudes toward giraffes. He wants to find out if there is something about their values and pastoralist way of life that makes them more amenable than settled farmers, for instance, to living alongside the huge animals, says O'Connor, who is also a freelance researcher for National Geographic magazine.
Elsewhere, where giraffes are on the brink, conservationists face unhappy choices.
"The park is a war zone," Fennessy says, a place where elephants are poached for ivory and giraffes for food.
"We're unsure about what's best to do. Should we set up a [giraffe] sanctuary near the park's headquarters or dart them and move them one by one out of the country?"
For the time being, the park employs people to follow the giraffes on motorbikes.
It's another risk that people will take to keep this much loved animal alive and well.
This story was updated on July 17 to add comment from John Doherty.
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