Nearly 530,000 people, including almost 30,000 people in Yorkshire, took part in the charity's annual Big Garden Birdwatch, the biggest wildlife survey in the world.
They counted more than 8.5 million birds, recording 73 species in 280,000 gardens – 18,000 in Yorkshire – across the UK over the weekend of January 30 and 31.
As predicted, small-bodied birds like the long-tailed tit, coal tit and goldcrest were the worst affected. Average numbers of all three species dropped significantly in Yorkshire since the 2009 survey.
Smaller birds like the long-tailed tit are particularly vulnerable to the cold, having to eat almost continuously to stay alive, the RSPB says.
According to the survey, the weather was also responsible for many more sightings of countryside birds like fieldfares, redwings, bullfinches and yellowhammers in gardens.
More usually found in fields and farmland trees and hedgerows, they have been visiting gardens for food.
Other members of the thrush family, including song thrush and mistle thrush, were seen in much higher numbers this year also looking for food.
Carolyn Jarvis, the RSPB's people engagement manager for northern England, said: "These results highlight the importance of feeding and gardening for wildlife, especially during prolonged cold periods."
In Yorkshire, the house sparrow was the most common bird with an average of 4.39 seen per garden. The blackbird and the starling came in second and third place respectively with averages of 3.62 and 3.28 per garden.
The figures came as the RSPB revealed its new sculpted gateway to a reservoir beauty spot that will welcome visitors – and keep out troublemakers.
Sculptor Mike Green was commissioned by the charity and water company United Utilities to design and craft the entrance to Dove Stone, Saddleworth.
He spent weeks designing the steel gate, which he welded and forged in his workshop at Mossley, near Manchester.
He said: "Dove Stone is a special place for me, as I'm sure it is for many local people. This allows me to leave a lasting and personal mark at Dove Stone."
The gate at the top end of the Dove Stone car park will be kept unlocked to allow members of the sailing club and residents access, but at weekends and bank holidays, it will be shut to cut congestion and stop people driving to the beach playing loud music.