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Second Broods Revealed an Early-Breeding Advantage in Urban and Forest Great Tits

Great tit feeding a chick at a nest box
Research · Reproduction & development

Great tits (Parus major) that began breeding early produced more fledglings across the full season in both forest and urban habitats, largely because they were more likely to raise a second brood. The 13-year study, first published in Journal of Animal Ecology on 26 May 2026, found that analyses limited to the first breeding attempt gave a different picture of the relationship between laying date and reproductive output.

Jérémy Defrance and colleagues monitored nest boxes from 2011 to 2023 in La Rouvière forest at Montarnaud and at eight urban study plots across Montpellier in southern France. They recorded first-clutch laying dates, clutch size, hatchlings and fledglings, and followed later breeding attempts through the end of each season.

Second broods changed the pattern

Urban females began their first clutches about 4.5 days earlier on average than forest females, and within Montpellier females in the most urbanised territories also began laying about 4.5 days earlier than females in the least urbanised territories. When only first broods were analysed, earlier laying tended to be associated with more fledglings in the forest but not in the urban habitats.

That pattern changed when second clutches were included. Earlier breeders had higher total annual fledgling production in both forest and city because they were more likely to breed again. In the city, the modelled probability of a second brood fell from about 66% for the earliest first clutches to almost zero for the latest; in the forest it fell from about 39% to 5%. The biological pathway was therefore largely indirect: an early first clutch increased the chance of a second brood, which increased the number of eggs produced across the season and ultimately the number of fledglings. Once clutch size was taken into account, the researchers found no evidence for a separate direct selection effect of first-clutch laying date.

Prey timing is a proposed mechanism

The authors hypothesise that differences in the timing and duration of food availability may help explain the pattern. Caterpillars are an important food for nestlings, and the forest and urban sites differ strongly in vegetation. The forest is dominated by deciduous and evergreen oaks, whereas the Montpellier plots contain a more heterogeneous mixture that includes pines, evergreen oaks and ornamental trees. The researchers propose that such differences could alter the seasonal availability of prey and the opportunity for a second brood, and call for direct comparisons of prey dynamics between habitats.

The study concludes that estimates of reproductive selection on breeding time can change when the full season is considered. In these populations, including second broods revealed an early-breeding advantage in both urban and forest environments that was less apparent when only the first nesting attempt was analysed.

Sources and image credit

  1. Defrance, J., Lambrechts, M. M., Fargevieille, A., Perret, S., Grégoire, A., & Charmantier, A. (2026). Beyond first clutches: Second broods reshape selection on breeding timing in forest and urban great tits. Journal of Animal Ecology, 95(7), 1163–1177. https://doi.org/10.1111/1365-2656.70284Primary peer-reviewed open-access study first published 26 May 2026. The authors analysed 13 years of breeding data from a forest plot at Montarnaud and eight urban plots in Montpellier, France. Earlier breeders had higher full-season fledgling production in both habitats, largely through a greater probability of raising a second brood.

Image: Jerzy Strzelecki / Wikimedia Commons — Great Tit feeding a chick at a nest box in Łódź, Poland, 19 May 2019; representative breeding image, not a bird from the southern France study · CC BY-SA 3.0 · Source

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