Age‐specific variation in reproduction is largely explained by the timing of territory establishment in the New Zealand stitchbird Notiomystis cincta

Abstract

Summary1. Using data from 327 nests over a consecutive 8-year period we examined age-specific variation in reproduction in a population of stitchbirds (or hihi) Notiomystis cincta and related how differences in reproductive performance were linked to the timing of territory establishment and breeding. 2. Across the population all reproductive parameters showed a quadratic relationship with an increase mainly between the first and second breeding season and a decline after the fourth year. A longitudinal analysis showed evidence of senescence by the sixth year in the numbers of chicks fledged and recruited. 3. Reproductive increases between years 1 and 2 were the result of poor-quality females dying after their first breeding season (differential selection hypothesis) in combination with surviving females showing improvements in reproduction in their second year (individual improvement/constraint hypothesis). 4. There was no effect of mate experience or territory quality on improvements in breeding between years. 5. The key variable influencing reproductive output was the timing of breeding. Birds that started laying earlier were more likely to lay multiple clutches in any given season. This was the main difference between first-year and older birds; generally first-year birds initiated egg laying later and consequently laid fewer clutches. 6. Approximately half of all first-year birds did not establish their territory until after the breeding season had begun. This delay in territory establishment resulted in these birds delaying breeding, which resulted in them having a lower reproductive output relative to all other birds. First-year birds that managed to establish their territory before breeding commenced, had similar rates of reproduction as older birds. 7. There was a positive relationship between the timing of territory establishment during a female's first year and her hatching date in the previous breeding season. We hypothesize that this was because late-hatched females were less able to effectively compete for territories against earlier-hatched members of their cohort, and this delayed their establishment and breeding in their first year. Thus, this social constraint is likely to be a major factor driving age-specific reproductive variation in this population.

Sense and sensitivity: responsiveness to offspring signals varies with the parents' potential to breed again

“…Few second clutches successfully yield fledglings, but those offspring that do survive to fledge are highly likely to recruit to the breeding population the following year [40]. Laying a second clutch is therefore a little like buying a ticket in a lottery, because it offers a low chance of a high-reproductive reward.…”

“…(a) Effect of carotenoid supplementation on adults Supplementation to parents increased the concentration of carotenoids circulating in the plasma (figure 1), and to a similar degree in each sex (LME: treatment, F Previous work has shown that naturally breeding hihi will sometimes attempt a second clutch during the breeding season, depending on environmental conditions and the timing of first clutches [40]. Few second clutches successfully yield fledglings, but those offspring that do survive to fledge are highly likely to recruit to the breeding population the following year [40].…”

“…We also included parental age in models because provisioning rules could be affected by age, with the current brood hypothesized to become of greater importance as parents senesce and reach their terminal investment [38,39]. In addition, maternal age can determine the breeding success in hihi [40]. All models were simplified using a backwards stepwise method until only terms that contributed significantly to the model remained.…”

Effect of supplementary feeding on reproductive success of hihi (stitchbird, Notiomystis cincta) at a mature forest reintroduction site

“…The lack of a strong age effect was unexpected, since previous studies have found that second-year and older females had improved reproductive success in comparison to first-year females, primarily due to delayed territory establishment in first-year birds (Armstrong et al 2002;Low et al 2007). The only suggestion of an age effect from our models, though at a non-significant level, was on first-clutch initiation.…”

“…Estimates from both groups are compared to literature reporting reproductive success from other hihi populations (nest success and number of fledglings produced; Makan et al 2014). We also incorporated age as a variable into our analysis, because previous studies on hihi found age to influence reproductive success (Armstrong et al 2002;Low et al 2007). …”