Reports and sightings of garden birds nesting unseasonably early are fuelling concerns that climate change is now beginning to alter the behaviour of some UK species.

Just days after the culmination of the RSPB's Big Garden Birdwatch, staff analysing early data from the citizen survey are worried about increasing numbers of recordings from people noting eggs and nests already occupied.

The charity says it is concerned these are early signs that milder winters are changing the behaviour of some of the UK's garden birds, many of which traditionally have nesting seasons that last between March and August.

Among the garden birds to have been found already raising offspring as early as the end of January is the Blackbird with reports of nests already occupied with nestlings - the name given to a bird not yet ready to leave which is yet to grow feathers and still has its eyes closed.

Alongside out-of-character behaviour, early nesting can present other problems for the baby birds as premature arrivals are then at huge risk of harm caused by changing temperatures if the winter weather takes a turn, combined with a shortage of food until spring really does start.

RSPB wildlife advisor, Katie Nethercoat explained: "From reports of Blue Tits checking out nest boxes and Robins gathering nesting materials, to Blackbirds and Woodpigeons already raising young, these are all signs that spring is on its way, albeit a little early.

"While this might sound like good news, it is in fact evidence that climate change is having an impact on wildlife right in front of our eyes. With nesting attempts occurring outside of the usual season, young birds could be at risk from sudden changes in temperature or faced with a shortage of food."

In response to increasing numbers of early signs of nesting birds, the RSPB is asking households to do their bit to protect new arrivals now at greater risk of harm until the weather warms up. Their advice includes:

1. Keeping up feeding to help parents support baby birds. This includes putting out easily accessible food such as mealworms and sunflower seeds to reduce the energy birds use trying to find food sources. Cleaning feeders regularly and ensuring a supply of fresh water can also help keep the birds in good condition through winter.

2. Help create a home. Nestboxes, alongside garden features like hedges, shrubs and trees, can help provide a sheltered spot for birds to raise their young. If deciding where to place a nestbox as a general rule of thumb, suggests the RSPB, they should face between north and east, avoiding strong sunlight and the wettest winds.

3: Do not disturb. With birds seemingly nesting in all kinds of weird and wonderful places the request is to check for nests before beginning any spring tidying in the garden. Nests are protected by law so if one is found it should be left exactly where it is and given a wide berth for a few weeks.