December 2015 was an extraordinary month in the UK from a weather point of view.

The average temperature was almost 8C, nearly 4C warmer than the long-term average for the month since records began. And it was also record-breaking in terms of rainfall.

This has been no ordinary start to the winter season, says meteorologist and BBC Weather forecaster Nick Miller: “It represents the warmest and wettest start to winter the UK has seen since records began in 1910.

“December should really be characterised by spells of colder weather and a greater frequency of frost,” says Miller.

While we did have a brief taste of a "normal" cold and frosty winter weather in mid-January, it has returned to the unseasonally mild conditions once again. However, according to the Met Office the longer forecast into February looks changeable with mild, wet spells interspersed with colder, drier interludes and the possibility of some longer, colder spells returning later in February.

And with extraordinary weather, you'd expect our wildlife would show out of the ordinary behaviours.

Typically, birds would be out foraging for enough food to provide them with the energy they require to keep warm and survive the cold night. For some small birds, such as the blue tit, that could be for as long as 85% of the daylight hours.

And as long as food is readily available, cold temperatures aren’t usually too much of an issue for our feathered friends. Downy feathers provide superb insulation and prevent heat loss, and for those birds that have come here from Arctic regions, they do so because our winters are actually relatively warm.

The main issue that we found from the continuing warm weather was that we continued to get reports of disease in garden birds

It’s finding the food they need that’s usually the difficulty as the ground becomes hard and water freezes over. The harsher the winter, the harder it becomes to get an easy meal in the countryside, forcing more birds into our gardens and the nuts and seeds left out for them.

But this season has been unseasonably mild, so are numbers of garden birds significantly down?

According to Clare Simm, Garden BirdWatch development officer for the British Trust for Ornithology (BTO), the mild conditions haven't stopped birds from coming into gardens in the way that would have been expected. But it has been noted that some species, such as blackbird, were seen in lower numbers than the same time last year.

“The main issue that we found from the continuing warm weather was that we continued to get reports of disease in garden birds, which the cold weather would normally kill off.

“Disease would affect all birds but it would probably affect garden birds more, as we encourage larger numbers of different species to congregate that wouldn't normally feed together in the wider countryside,” explains Simm.

Beyond our gardens and into the wider countryside, the warm December begins to tell a different story.

Numbers of winter migrants – birds such as redwing, fieldfare and some geese – have been low, explains Simm, and we’ve had several unusual winter visitors, like the first red-rumped swallow to ever be recorded in Britain in December.

In fact, other species that don’t normally make an appearance until summer – whinchat, wheatear and swifts – have also been reported.

While little is known about how this unseasonably warm weather has affected birds of prey and owls, Simm theorises that you might expect more rodents to be around, which would normally be somewhere warm if it was colder, providing an unexpected food source for these meat-eaters.

Winter storms "Desmond", "Eva" and "Frank" have also had an influence on our bird life. The high winds, she says, “have produced lots of wrecked seabirds along the coast, many of which have been blown far off course”.

Measuring the impact

The recent cold snap and some snow has, says Nick Miller, "brought a return to more typical weather conditions for January". The BTO also received reports of bird numbers increasing in gardens in search of food and shelter, as might be expected.

And if the temperatures had remained low, it may have affected our migrant thrushes. Winter visitors like fieldfare and redwing are able to find most of their food in the wider countryside. As the temperature drops and food becomes scarce or covered by snow, these birds increasingly rely on food provided in our gardens.

“There are still migrant birds arriving in the wider countryside, such as Bewick’s swans – this could be evidence of birds making the 'hop' across the North Sea in response to the colder weather,” Ms Simm told BBC Earth.

But as the warm and wet weather is set to continue, how it is truly affecting British birds is not yet known. You, however, can help build a picture of the effect of this year's warm and wet winter by taking part in this weekend’s Big Garden Birdwatch, the annual monitor of bird numbers and other wildlife run by the Royal Society for the Protection of Birds (RSPB).

Richard Bashford, campaign projects manager for the RSPB predicts fewer countryside birds will probably be recorded, as they tend to only come into our gardens after prolonged periods of cold but points out that every year is different and while individual years are interesting to note, it's important to monitor the ongoing trends.

“Because the birdwatch has been carried out for 36 years, occasional mild or harsh winters will result in varying numbers of birds being seen. However, we look at the long term trend for each species since the survey began in 1979 rather than between year trends since this paints a more accurate picture of how our birds are faring.”

And he adds that if the weather were to become a lot colder in late January, as is "the norm", putting out food and water in readiness should attract larger numbers of finches, tits and thrushes coming into our gardens.

Whether you see lots of birds or see none at all, it's really important for as many people as possible to take part in the RSPB's Big Garden Birdwatch this weekend and help to measure the impact of the weather. And if this weekend gets you hooked on staring at your feeders there is also the BTO's year-long Garden BirdWatch to take part in.

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Jeremy Coles is a feature writer for BBC Earth. He is @jpcoles on Twitter.