Maria's calf's jailbreak

Last evening I let the three cows, their calves and Muscles out of the fruit tree area and into the NE pasture.  This afternoon Maria was mooing in the corral.  I then discovered that her calf was in the backyard.  I guess he is taking after his dad, Toby.  I let the calf back into the corral to be able to drink from his mother.  I don't know how he got out of the corral.  Did he crawl under the corral fence?