Overview

The evidence for global climate change and for its underlying anthropogenic causes is gathering rapidly. Over the past 11 years the active growing season of plants has advanced by roughly 8 days in northern latitudes1. This evidence for increased photosynthetic activity is supported by the positive trend in the amplitude of the seasonal cycle in atmospheric CO2 (ref. 2). The phenology of animal populations should also be affected by climate change, but to date there has been little evidence of this. Here we report that long-term trends in the seasonal distributions of laying dates of birds in the United Kingdom show a tendency towards earlier laying, consistent with the changes reported in growing season.