Loads of British birds are laying their eggs earlier every year and experts think it's all down to climate change.
A study by wildlife groups found some robins, tits and finches are laying earlier than they were 40 years ago.
Birds' nesting and migration habits are also changing and experts think it's because they're trying to react to changes in our weather to survive.
Hundreds of volunteers check thousands of nests every year to get an up-to-date snapshot of birdlife in the UK.
The RSPB bird charity, which is one of the wildlife groups involved in the study, said the findings showed climate change was already with us.
Dr Mark Avery, from the charity, said: "From our gardens to our seas, birds are having to respond rapidly to climate change simply to survive.
"As often before, birds are acting like the canaries in a mine shaft and giving us early warning of dangerous change."