Why is this deer licking a fox ?

TLDR : We don't know.

Was the buck simply nibbling on a plant behind the fox? Had the fox happened to hop in front of the buck’s face? Lowe dashed into his apartment to grab his camera, and made it to the window to catch the deer taking another lick. The fox, docile in the shade of its antlered friend, wasn’t just tolerating the apparent cleaning, Lowe realized. “It looked like it was actually enjoying this,” he says.

There’s a temptation to describe their interactions as mutually beneficial, in line with the natural world’s other astounding instances of species-to-species symbiosis. When Lowe first saw the buck and fox together, for example, he was reminded of underwater “safe zones,” where “predators and prey all line up to get cleaned” by small fish that munch on parasites... Neither Cove nor Roemer, who spent years studying island foxes earlier in his career, however, are convinced licking does much for the ecological fitness of deer, foxes, or cats.

Both researchers suggested what might be a more obvious benefit for the foxes and cats: Getting licked feels good. “Maybe deer are getting those hard to reach places,” Cove says. As for the deer, ocean breezes cover islands—foxes and cats included—in salt. Cove has a theory that deer on islands particularly might be lured into the cleanings by a little extra seasoning.

Roemer doesn’t buy the salt theory, either: If plants and rocks are also coated by the breeze, he reasons, it wouldn’t make sense for a deer to go through the trouble of tracking down a moving, claw-possessing island resident for tastiness alone.

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