Data from: Double brooding in house wrens is repeatable but constrained by time-of-season

Birds in some species produce two broods in a season to maximize
reproductive success, but in species such as the northern house wren
(Troglodytes aedon), not all individuals produce a second brood even if
they have enough time to do so. We investigated whether variation in
individual quality, in addition to time-of-season, explains some of the
variation in the likelihood of producing a second brood. We examined the
effects of individual age, body condition, and territory quality, and
estimated the repeatability of producing a second brood using breeding
records from a long-term dataset. We also cross-fostered eggs between
earlier-nesting females (presumed high quality) and later-nesting females
(presumed low quality) to delay or advance the natural nesting date,
exposing an effect of quality if present. There was little evidence that
the individual traits measured affected the production of a second brood.
Cross-fostered, delayed females did not differ from the control in their
likelihood of producing a second brood, but advanced females were more
likely to produce a second brood compared with the control. However, the
production of a second brood was significantly repeatable, and this
repeatability was substantially higher after accounting for variation in
timing of the first brood. This suggests that individual characteristics,
in addition to time-of-season, have a substantial effect on the likelihood
of producing a second brood, but that further studies are needed to
identify the specific traits responsible for this effect.