The British Trust for Ornithology analysed nest-laying records for 65 native species from 1971 to last year, kept by hundreds of dedicated amateur ornithologists.
It found that for 20 of those species, the average date when the first egg was laid became significantly earlier over the 25 years, and for only one species, the stock dove, did that date become significantly later.
For the remainder of the birds, no strong trend in egg-laying dates emerged - although there was a weak, overall tendency towards earlier clutches. Warmth earlier in the year makes plants and insects grow more rapidly, which provides more food for baby birds - thus there is competitive advantage in earlier egg-laying. The research is published in this week's issue of the science journal Nature.Reuse content