Staff at Hatton Country World in Warwickshire couldn't understand why they suddenly had 100 pregnant guinea pigs on their hands - until they released one of the male rodents had managed to escape his enclosure and infiltrate the female-only enclosure.
They noticed that the exhausted father-to-be, now nicknamed Randy, had lost a little weight, but did not realise why until they discovered he was actually a male rodent being kept busy in the wrong pen.
The animal park, which already has 300 male and female guinea pigs, is now readying itself for a population boom in the next few weeks.
Manager Richard Craddock said: "One of our male guinea pigs managed to find his way into the female enclosure and had a very good time by the looks of it.
"We suspect a child may have placed him back in the wrong pen by accident after stroking him or Randy may have somehow broken out of his enclosure to get to the females. "
"We believe that the newly-named Randy could have impregnated up to 100 female guinea pigs, which have litters of about four, so if you do the maths we could be expecting quite a baby boom.