For more than 40 years the Royal Society of Protection for Birds (RSPB) has been asking people to monitor the birds in their own gardens to help them track how well different bird species are doing in Britain.
The RSPB asked everyone taking part to spend an hour outside counting and identifying all the birds they can see in their own garden, or from a balcony or window. Young and old joined in with some care homes taking part and some schools setting it as homework.
We've created a "bird box" on Shooglebox to showcase some of the fun and colourful tweets we spotted across social media over the weekend.
Bird photographer Carl captured this amazing photo of a robin in flight during the Big Garden Birdwatch. He tweeted: "Took this photo today, one of my favourite ever Robin pics."
Some people reported fewer sightings than usual and blamed a variety of different reasons – this person spotted a bird of prey that might be keeping them away. Others blamed building work, neighbourhood cats, Storm Malik and dwindling food sources. Quite a few people reported seeing lots of birds in their garden ... until they tried to count them!
TV presenter Michaela Strachan tweeted a photo of her and her mum taking part, reporting a drop in the number of birds in her mum's garden: "Sadly she says most of her birds have vanished in the last 2 years. She used to get loads. All we saw today was a wood pigeon and a robin. Disappointing but important data for the RSPB @BBCWinterwatch"
The CEO of Compassion in World Farming (CiWF) Philip Lymbery tweeted about how important the Big Garden Birdwatch is, saying: "The declines in our birds and wildlife are widely accepted as being driven by agricultural intensification and the resulting deterioration of farmland habitats. Nature needs us."
You can see more social media post embeds in this read-only Shooglebox.