It is part of a national initiative to monitor key bird species.
Hundreds of people around the world have been following the daily trials and tribulations of the three chicks, which hatched around six weeks ago in a specially designed owl box at a site near Midhurst.
The box is one of dozens provided by the South Downs National Park Authority and Sussex Ornithological Society to help support the birds of prey.
Ornithologist Graham Roberts joined National Park ranger Angela Ward as the three owlets were ringed near their home at a barn near Midhurst.
Graham also weighed the chicks and took measurements, including the length of their wing feathers.
Graham has a special licence to carry out ringing and works for Sussex Ornithological Society.
He said: “Barn owls have been nesting at this particular barn for many years in the box provided by the South Downs National Park Authority.
“It’s been great to watch the chicks live on the webcam and now see them for real.
“We have three young this year from the five eggs that were laid.
“The number of young tends to be determined by whether it’s a good year for voles or not and this year has been pretty good.
“We have three healthy chicks, varying in age from five and a half weeks to six and a half weeks.”
Graham explained the importance of ringing.
“In Britain we’ve had a ringing scheme for over 100 years,” he said.
“It’s the oldest in the world and is co-ordinated by the British Trust for Ornithology.
“Ringers are highly-trained and licensed to do this activity.
“As barn owls are at the top of the food chain it’s important to monitor their success and record populations throughout the country.
“In this case for these chicks the ring will stay on the bird for life.
“Each ring has a unique number so if anybody finds that bird and sees the ring, they can report it and get a history of that bird sent to them.”
There are 97 barn owl boxes spread across the Wealden heath area.
This stretches from Petersfield to Pulborough.
There are dozens more across the rest of the South Downs National Park.
Angela, Wealden Heath Ranger, said: “Barn owls are just amazing.
“Obviously they are lovely to look at, but I think they’re also a really iconic species of our countryside.
“They’re a good indicator of the health of landscape.
“As a general rule the more barn owls we have, the healthier the eco-system is.
“Landowners have a great affinity with barn owls because a long time ago they very often had an owl loft in a barn, but many of those barns have been converted or lost over the years.
“Most of the landowners are very keen to have barn owls back and put up nest boxes, but they don’t have always have the time to.
“That’s where the National Park comes, in advising landowners on nesting sites and boxes.
“It’s also helps us talk to landowners about habitat for barn owls, as well as all sorts of other species such as ground nesting birds, small mammals and everything going up into the food chain, with barn owls at the top of the food chain.”
To keep track of the progress of the barn owls, you can join the hundreds of people watching and tune in to the South Downs National Park Barn Owl Watch at https://www.carnyx.tv/LiveCameras/WildlifeCameras/BarnOwl.aspx