Since the Big Garden Birdwatch began in 1979, the average number of starlings spotted by participants has dropped from 15 to just three.
Although the species was the number two “most spotted” bird, it was seen in fewer than half of UK gardens.
The British Trust for Ornithology (BTO) confirmed that starlings were a “conservation concern”.
The RSPB and its partners are currently carrying out research to find out the reasons behind the decline.
As Dr Rob Robinson from the BTO explanied, studies so far point to a decline of traditional, established pastures as a major threat to the birds.
Intensively farmed land, he told BBC Nature, made it more difficult for the birds to find their favourite food – cranefly larvae that live in undisturbed soil.
“These days, farmers are tending to cultivate in short rotations,” he explained, “putting a field down to grass for three to five years and heavily fertilising it.
“Another factor… is harvesting efficiency. Thirty years ago, the farmer would leave 1% of grain on the field. But now the harvesting efficiency is 99.9%, which leaves very little for the birds.”
In England, conservation groups including the RSPB and the BTO are working with Natural England to provide advice for environmental stewardship schemes. These schemes provide funding for farmers in England to deliver effective environmental management on their land.
Another problem that has been highlighted is a change in modern building design; starlings often nest in cavities and crevices in old buildings.
“They’re very noisy and messy, so many people block up those spaces to prevent them nesting,” explained Dr Robinson.
He suggested that “a very positive thing” people could do to help the birds would be to put up nesting boxes.
The RSPB said that more people took part in this year’s survey than ever before, with almost 600,000 people counting more than nine million birds of 70 different species.
The charity said the survey was a very useful “snapshot” of the health of British birds.