There is a story by the guy who made this picture and its written up on furaffinity here it is so some people get a clue on whats going on.....

Frank and Clayton

they always stuck together, did everything together
dated women together, fucked women together
but frank had a little...secret

that is till one day Clayton came home early one day
only to find Frank getting the bottom knock out of his ass

Clay didnt know what to do, the two hadnt even heard him come in
he was furious at his powerful brother being taken by some skinny queer
but something stirred in his jeans, his cock was about to burst from his
pants. he pulled it out and started jerking it to the sounds of the
bird's huge balls smacking on his brother's ass, it felt so good
he had to get closer, he could see the bird's hole appearing and re-appearing
as its cock disappeared in his brothers clearly used hole
Clayton was mesmerized by the sight, he was so close
to cumming he could barely take it anymore
thoughts racing "im not gay, im not some fag....FFFFFFFFFFF!"
he snuck up and shoved his entire girth deep in the birds flexing hole
the bird gasped, and stopped, looking back his eyes full of terror
seeing clayton there "i didnt mean to..i swear!" pulling out, clayton
stopped him. "shut the fuck up queer....n keep going"