POLOKWANE, SOUTH AFRICA—After three rainy seasons together, a black rhinoceros and a parasite-eating tickbird are beginning to suspect that their symbiotic relationship has fallen into a rut, the couple reported Sunday. 

"We're really symbiotic—almost too symbiotic," the rhino said. "It's just gotten so predictable lately that I'm starting to wonder, 'Is this all there is?'"

The rhino and tickbird pass another morning on the African savannah not saying one word to each other.

First meeting at a local watering hole in 2004, both creatures immediately saw themselves as natural for one other and, in the words of the rhino, felt something "new, gratifying, and mutually beneficial." Within hours, the tickbird had moved into the rhino's habitat and set up house on his thick hide. 

But as time went on, it slowly dawned on the couple that their partnership was perhaps merely one of convenience.

 "I admit, when we first got together, I was a total mess," the rhino said. "She really helped me clean up my act. But we've been together so long now that I always know exactly what she's going to do next."

Devouring horsefly larvae embedded in her 3,000-pound partner's back, the tickbird seemed to agree that there was little fire left in their symbiotic relationship. At worst, she said, it feels like she and the rhino have been trapped in the same dead-end symbiosis for "countless millions of years."

"We just go through the motions, and there's hardly any communication," the tickbird said. "And we do it the exact same way every time. I get on top and take the parasites off while he just lays there."

"Feed off the embedded ticks on his hide, chirp when the predators come. Feed off the embedded ticks on his hide, chirp when the predators come. Where's the passion, the heat?" the tickbird continued.

The tickbird also accused the rhino of trying to make her "feel small." 

"He doesn't realize everything I do for him," the tickbird said. "If it wasn't for my 'incessant squawking,' as he calls it, he would be shot by poachers before he even saw them coming." 

Both creatures separately expressed envy of their neighbors, a plover and crocodile, who "never seem to have the problems we do," the rhino said. 

"That crocodile appreciates having his teeth cleaned, and he makes sure she knows," the tickbird said. "Look at that big grin."

The rhino said that he often feels like a victim of her nitpicking.

"I might look tough, but I have feelings," the rhino said. "I give her plenty to eat and a great place to perch, but it feels like she's constantly pecking an open wound. Ugh, why can't we just be friends with mutualistic benefits?" 

The frustration has caused the pair to act out in passive-aggressive ways. The rhino will frequently charge without warning, jarring the tickbird from her perch. Meanwhile, the tickbird often deliberately embarrasses her partner by speculating aloud about a symbiotic relationship with a cape buffalo or zebra, often within earshot of those species.

According to a nearby elephant, this sense of stagnancy commonly occurs in symbiotic partnerships across sub-Saharan Africa.

"The rhino and tickbird may have evolved physiologically to meet each other's needs, but it's clear they haven't evolved emotionally," the elephant said. "They need to recognize that in order to go forward. The rhino's loud snorting  is very alienating. And obviously the tickbird is projecting her own feelings of inadequacy when she criticizes the rhino for being a typical Diceros bicornis."

For all their friction, both creatures conceded that they weren't sure they could actually live without each other. 

"I don't know why we stay together," the rhino said. "I guess we're just creatures of instinctual habit."