The best way to guarantee breakfast in bed for some small African birds is falling asleep on your dinner plate—even if it's a giraffe's armpit.

Scientists have long known that yellow-billed oxpeckers hang out on massive African mammals like giraffe, water buffalo, and eland during the day—an often beneficial relationship that provides hosts with cleaner, healthier skin. These small brown birds can often be seen perched on top or hanging off the animals, picking through their hair in search of tasty parasites like ticks.

But a series of rare photos from a large multi-year camera trap study in Tanzania's Serengeti National Park have revealed that the birds actually roost on some of their hosts overnight. The National Geographic Society provided funding for the project, called Snapshot Serengeti, which is led by lion expert Craig Packer. (See how hidden cameras reveal the secret lives of the Serengeti.)

"You look at them on the giraffe and they're just right up in there," says Meredith Palmer, a Ph.D. candidate in behavioral ecology at the University of Minnesota. "It's a very safe, comfortable place for the birds."

Palmer, who led a new study on these giraffe "bed and breakfasts" in the African Journal of Ecology, believes the roosting may also be a territorial maneuver to deter competitors.

View Images Yellow-billed oxpeckers sleep on a giraffe in this nighttime camera trap picture. Photograph Courtesy of Meredith Palmer

Their close cousin the red-billed oxpecker is smaller with a more versatile beak, allowing it to feast on the parasites plaguing a bigger repertoire of hosts, such as zebra, impala, and wildebeest.

Because the yellow-billed oxpecker has a more limited menu, it makes sense that it would keep a closer grip on its daily bread—even if it means sleeping on it.

"Once you find [a host], it's worth just sticking around so it doesn't wander off," she says.

Strange Bedfellows

Yellow-billed oxpeckers nest in trees or other vegetation when it's time to lay their eggs. But the rest of the time they're perfectly happy dangling from a giraffe—sometimes, seven birds are seen clustered in a single armpit.

"I imagine it's got to be pretty scratchy with seven birds hanging off you," quips Palmer.

Tiffany Plantan, who has studied oxpeckers but was not involved in Palmer's study, praised the paper, saying "this is, as far as I know, the first study examining these birds' behavior at night."

Animal Selfies From the Serengeti How do you get the best animal selfies? To get one-of-a-kind images, a team led by National Geographic grantee and photographer Craig Packer installs camera traps all around the Serengeti that automatically take photos when animals wander close enough to trigger them.

"It's opening the door for a whole slew of questions that can be asked, particularly between the differences between the two species of oxpeckers and their nocturnal behavior," says Plantan, an ecologist at the University of Miami. (Read why birds matter in National Geographic magazine.)

She has seen red-billed oxpeckers take naps on buffalo and other animals during the day, but she had never seen the behavior at night. Likewise, the Serengeti camera traps have also not caught red-billed oxpeckers roosting on their hosts.

View Images Yellow-billed oxpeckers sit on the head of a water buffalo. Photograph by Beverly Joubert, Nat Geo Image Collection

Another difference is that red-billed oxpeckers have smaller, more scissor-like beaks than yellow bills, which enables each species to eat different tick species.

Side Dish of Snot

The birds' palates don't consist only of blood-sucking parasites, however. Oxpeckers feast on a whole range of their hosts' bodily fluids, including mucus, blood, and even snot.

"They’ll go in the goop that's in eyes, they'll go in the secretions from the nose and the mouth. They're opportunists," Plantan says. (Read: "How 2 Million Pounds of Rotting Flesh Helps the Serengeti.")

But the relationship may not be entirely mutual. Red-billed oxpeckers have some vampire-like characteristics, often digging into their hosts' open wounds. Plantan says she has even seen red bills puncturing donkey hides with their beaks, woodpecker-style, to get at their blood.

Surprisingly, the host animals are often apathetic to this treatment. "A lot of the times they would just ignore the birds, even when they were wound-feeding," Plantan says.