The pair hatched five eggs in their second attempt after failing to produce any young last year, though one cygnet was killed by local wildlife.
RSPB Shetland warden Helen Moncrieff said it was “fantastic news” for Shetland’s population of the amber-listed species, which they had been trying to protect from being disturbed by visitors to the popular loch over the past few months.
She said they would stay as a family until late winter or early spring before the cygnets start fending for themselves.
The history of breeding whooper swans at Loch of Spiggie began in 1907 when a wounded bird was brought from nearby Loch of Clumlie to join another maimed bird.
The pair first bred in 1910 and continued irregularly until the end of the First World War, only to be shot in 1920.
“Some whooper swans remain in Shetland all year round, with breeding attempts occurring annually since 1994 - but this is the first time we’ve seen a pair successfully produce baby whooper swans at Loch of Spiggie. To think it’s taken almost a century makes it all the more remarkable,” Moncrieff said.