Data from: Changes in breeding phenology and population size of birds

1. Although the phenology of numerous organisms has advanced significantly
in response to recent climate change, the life history and population
consequences of earlier reproduction remain poorly understood. 2. We
analyzed extensive data on temporal change in laying date and clutch size
of birds from Europe and North America to test whether these changes were
related to recent trends in population size. 3. Across studies, laying
date advanced significantly while clutch size did not change. However,
within populations, change in laying date and change in clutch size were
positively correlated, implying that species that advanced their laying
date the most were also those that increased their clutch size the most.
4. Greater advances in laying date were associated with species that had
multiple broods per season, lived in non-agricultural habitats and were
herbivorous or predatory. The duration of the breeding season increased
for multi-brooded species and decreased for single-brooded species. In
contrast to studies of changes in spring arrival dates (for migratory
species), the changes we found in laying date and clutch size were not
related to changes in population size (for resident or migratory species).
5. This suggests that, across a wide variety of species, mismatches in the
timing of egg-laying or numbers of offspring have had relatively little
influence on population size compared with other aspects of phenology and
life history.