Uh, OK. You're not sure what that's about, but you grab it, because the first life lesson gamers learn as children is to steal everything they see. Unfortunately it's still daytime, so you keep wandering until the egg hatches into a full-grown owl that doesn't object to being stuffed in your trousers.
Oh, well now it's obvious. You take the owl out of your pants at the laser gate, because its gentle hoots will convince the guard that it's nighttime. Wait, what?
"It's owl o'clock already?!"
Remember, you're battling what is supposed to be an elite military unit. And yet apparently their soldiers tell time not with carefully calibrated wristwatches but by the calls of the local avians. "What do you mean the sun's still beating down on us? Didn't you hear the owl?"
Shockingly, these sorts of puzzles didn't make it into later Metal Gear games, because few gamers would think to resort to Doctor Dolittle antics in the middle of a war zone.