People start trimming their hedges at this time of year once the breeding season is over but the RSPB said delaying the annual pruning of greenery was even more important this year than normal.
The conservation charity said milder weather this autumn had meant birds were still eating available insects and many hedgerows were still covered in berries.
Many species rely on the fruits to set them up for the lean, cold winter months, with the vital natural food source particularly important after the first frosts when they become softer.
The RSPB is urging gardeners, councils and farmers not to cut hedges until later in the winter, or even early spring, when all the berries have been eaten.
They also suggested cutting hedges on rotation - as trimming some species every year prevents the plants from producing large amounts of berries - which would benefit species such as bullfinches, song thrushes and redwings.
Richard James, RSPB wildlife adviser, said: ''The autumn berry and fruit crop is an important food source for many birds. If cutting can be put off until later in the year it can help provide our birds with an additional food supply.
''Usually once any late nesters have flown the nest we would say it was a good time to start tidying hedgerows and trimming bushes and shrubs. They can get straggly and when they are stripped bare of berries they are of less use to birds.
''We'd urge anyone thinking of a tidy up to wait just a few more weeks until the natural food has been eaten.''
