Two adult night herons and two recently fledged juveniles were photographed at a Somerset reserve by Graham Hall.
Mr Hall said he photographed the two birds from half a mile away to test his camera and was "blown away" when he realised they were night herons.
Somerset Wildlife Trust said it showed for the first time in recorded history that night herons have bred in the UK.
Black-crowned night herons are rare in the south of England, according to experts, with only around a dozen spotted in Somerset since the 1800s.
It is thought the adults either bred at the Somerset Wildlife Trust's Westhay Moor national nature reserve or the nearby Avalon Marshes site.
Mr Graham was getting ready to pack up at the reserve when his friend pointed out two birds roosting half a mile away in a tree.
"I thought that would be an interesting shot and a challenge for the camera," he added.
"We thought they were bitterns but when I zoomed in - blow me - they weren't bitterns.
"I've never seen a night heron in the wild before and two birds together can only mean one thing."
Kevin Rylands, RSPB conservationist officer, said: "They are a native bird and in the past there have been some free-flying night herons around Edinburgh Zoo.
"But they have never bred here before in the wild so this is a first."
Roger Dickey, from the Somerset Ornithological Society, said it was "terribly exciting news".
"Night herons are one of southern England's rarer summer visitors.
"That they have decided to breed here for the first time on record confirms the Avalon Marshes' significance as one of the UK's most important breeding areas."

Met Police officers are also searching a property in Southwark, London, where they have found human remains.
Westminster officer Gordon Semple, 59, from Greenhithe, Kent, was last seen on 1 April in the London Bridge area.
Police said his family had been informed about the "significant development".
A spokesman said: "We are unable to make formal identification at this stage, but this is devastating news for all those involved in the search for Gordon."
Police who were called to an address on the Peabody Estate on Thursday afternoon found human remains, he said.
He said forensic work was under way at the scene which may take some time.
A post-mortem examination would be held in due course, he added.
He said police would not speculate about what had happened or any possible motive at this stage, and would not speculate on the cause of death until post-mortem tests had taken place.
On 1 April, PC Semple, who is originally from Inverness, had a work meeting at the Shard's Shangri-La hotel and left at about 12:30 BST.
He was seen on CCTV in Great Guildford Street at 15:00 BST and his partner reported him missing later that night.
PC Semple has no children but still has family in Scotland.
The man under arrest is being held in custody.

Samantha Jenkins, 19, from Llanelli, fell into a coma and died in 2011.
Her inquest heard she had low mineral levels, which may have been the result of malabsorption caused by chewing gum.
Maria Morgan told BBC's Jason Mohammad programme: "It's something that happens over a period of time - eight or 10 months."
After her death, Mrs Morgan said she found receipts showing Miss Jenkins had been buying chewing gum almost every day.
"The pathologist said it was going down a road he doesn't know enough about, but he said there was enough evidence there to say it was a huge thing that it could be."
Her husband, Wayne Morgan, said they believed Miss Jenkins's death could be linked to sweeteners used in chewing gum.
Colin Phillips, acting senior coroner for Swansea, said the cause of death was a shortage of oxygen to her brain, resulting from a convulsion caused by an imbalance of minerals in her body.
"The chewing gum inside her system did not end her life, but it's a possibility the over consumption of sorbitol and aspartame was the result of all her salts going low and that's what ended her life," said Mrs Morgan.
A pair of nocturnal herons has bred in the wild in the UK for the first time, conservationists have revealed.
[NEXT_CONCEPT]
Detectives searching for a serving police officer who has been missing for six days have arrested a 49-year-old man on suspicion of murder.
[NEXT_CONCEPT]
The mother of a Carmarthenshire teenager whose death may have been caused by chewing gum wants families to be aware of the potential dangers.