They could be called "oxterpeckers"

As reported by National Geographic:

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...

"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."..

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. 

Re my tongue-in-cheek title for the post:

Definition of "oxter" - chiefly Scotland and Ireland : armpit. (etymology: Middle English (Scots), alteration of Old English ōxta; akin to Old English eax axis, axle).

Photo credit Meredith Palmer.