Studies have shown that feeding birds in spring and early summer does increase the success rate of nesting birds especially when weather conditions such as cold, wet weather in spring make foraging for natural foods more difficult.
Regular feeding throughout the year will ensure that birds become accustomed to the sites of feeders and bird tables.
Natural foods for many species are at a peak in late summer and early autumn and this is probably the time when birds benefit least from supplementary feeding but continuing to feed suitable foods will do no harm.
Avoid feeding peanuts from feeders that allow whole nuts to be taken during the breeding season to avoid any chance of young birds being choked.
Adult birds will keep themselves in good condition by using your bird feeders but continue to forage for appropriate food such as invertebrates to feed their young.
Winter feeding, especially during cold spells, can be a lifeline for many birds. As well as providing supplementary foods from feeders it's well worth also managing the habitats in your garden to provide more natural foods (see questions on wildlife gardening for further information).