This occurs more often than most of us think.
As a side note, there is a one anltered cow elk in my 700+ animal research herd. I could not determine whether this cow had ever been pregant, never saw her a calf. In three years I've never seen the antler when it wasn't in velvet.
Mature bull elk (without a harem) frequently pair up and mount each other, generally with one bull doing most of the mounting. I'm assuming the "mountor" is dominant over the "mountee." However, turnabout seems to be fair play with some of these "pairs" with the "mountee" becoming the "mountor."
Geez, that sounds bad.

I hope I haven't offended any of those guys north of the border, especially those guys in the red coats. (I better leave this alone before it gets worse.) [&:]
I've never noticed penetration by these bulls. Mounting usually lasts no more than a minute. The pairs may spend hours together, I didn't keep check to see if they stayed together for more than a few hours.
I've got lots of interesting nd informative deer, elk, turkey, duck and goose biology/behavior and hunting techniques/tips on the "T.R.'s Tips" board if you guys are interested. Come on over and join us.
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Good hunting and I hope you all have a Merry Xmas,
T.R.