Life-history trade-offs, density, lay date—not personality—explain multibroodedness in great tits

In various taxa, multibroodedness is a common breeding strategy.
Life-history theory predicts that individuals can increase fitness by
producing multiple broods within a season. Despite the apparent increase
in the number of offspring parents might produce per season, not all
individuals are multibrooded, suggesting a trade-off. We studied
ecological and behavioral factors influencing the initiation of second
clutches in great tits (Parus major), an optionally multibrooded bird
species, by distinguishing two types of clutches: replacement vs. true
second clutches, produced after failure vs. successful first breeding
attempts, respectively. We predicted that lay date, density, and
investment in first clutches would decrease the probability of initiating
a second clutch, but that faster exploring behavioral types with a faster
pace-of-life would be more likely to be multibrooded. The probability of
initiating true second clutches varied negatively within-individuals with
lay date and breeding density. The initiation of replacement clutches
instead varied negatively among-individuals with lay date and density,
suggesting non-random settlement of behavioral types across environments.
Individuals were less likely to be multibrooded when producing many
offspring from their first clutch, suggesting within-year reproductive
trade-offs, similar to previous studies. No previous research has linked
personality to multibroodedness; here we show that neither the repeatable
nor the plastic part of an individual’s exploratory behavior predicted
multibroodedness. We confirmed our prediction that the resolution of
trade-offs may occur either at the within- or among-individual level. Our
research contributes to the understanding of life-history evolution in the
wild by studying the mechanisms shaping multibroodedness within seasons.
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