Reece Oliver, 27, was targeted by members of the public outside his home after he discovered the two Humboldt penguins he had bought had been taken from a zoo.
Mr Oliver, a show jumper who keeps other exotic animals, bought the two penguins in early January after seeing them advertised on Facebook.
But he discovered the pair - who he named Pablo and Penny - had been stolen from a zoo when he checked their microchips on a database.
The animal lover, from Strelley, said: "I purchased them from somewhere where they were pretty badly looked after.
“I saw them online - a man offered them to me on a Facebook group.
“I bought them and they arrived at the beginning of January. They were in quite bad health.
“I had about £1,000 in vet’s fees. They were put on some medication.
“I ran the microchip number on a zoo database, and it came up as stolen."
He alerted the zoo as well as the police.
But after the police announced they had arrested a suspect for stealing the penguins, members of the public came to Mr Oliver’s house and shouted abuse at him.
He said: "Two or three people came to the house.
“They were shouting ‘penguin thief’ and abusive things. When it comes to animals, people get their backs up.
“Everything we keep, we keep to a very high standard. It’s not like we keep them in a bad way.
“The penguins were in bad health. I think if they had remained with the man we bought them from, they would have died.
“Penny was suffering from aspergillosis, a fungal infection which gets in the lungs.
“They are back at the zoo now. We will stay in contact.
“With Penny, it’s 50/50 whether she will survive.”
Police said the penguins were stolen from the zoo in November.
A 23-year-old man from Preston was arrested on suspicion of burglary and theft, and has been released under investigation.
Sergeant Andrew Browning, of Nottinghamshire Police, who worked on the investigation, said: “My first thought was this is one for the books, and one to tell the grandkids, because there's no way we thought we would go down there and actually find two penguins.
“It was an unusual one. Even when we went down to custody it made everyone laugh, particularly the custody sergeant who was booking us in.
“It was a real off-the-wall find.”