DOI: 10.5061/dryad.8931zcrqx
title: Life-history trade-offs, density, lay date—not personality—explain multibroodedness in great tits

description: 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.
 --
description: Data were collected from 12 great tit nest-box plots near Munich, Germany (47858°N, 11814°E), monitored between 2010 and 2017. Each plot was composed of 50 nest-boxes placed in a regular grid, covering an area of approximately 9-12 ha. Nest-boxes were monitored throughout the breeding season (April-July) at least once per week to record lay date (back-calculated assuming one egg was laid per day), clutch size, onset of incubation, hatching and fledging date, and the number of fledglings. Breeders were caught in the nest-box using spring traps, and banded with a metal band if not previously banded, when their nestlings were 7-12 days old. We thus were able to determine whether, within a breeding season, pairs initiated a second clutch, and whether it was a replacement or a true second clutch. A replacement clutch is here defined as a clutch initiated after the failure of the pair (identified by bands) to produce fledglings from their first brood within the focal year. Since we could not identify individuals that failed prior to capture, we had to exclude nests that failed before hatching (n = 241 nests), or when nestlings were less than 7 days old (n = 135 nests).