Timing of adult remigial wing molt in female Black Brant (Branta bernicla nigricans)

Abstract

Timing of molt is a critical life-history trait because molt is a nutritionally demanding process that must be completed before fall migration. We used data from 1992-2008 to assess hypotheses that initiation of the prebasic molt by Black Brant (Branta bernicla nigricans) was ultimately controlled by (1) the need to complete the molt before fall migration and (2) advantages of restoring depleted nutrient reserves before growing feathers. Specifically, we expected molt to occur sooner after hatching in years when nesting was delayed (prediction 1), but we expected individuals to delay molt in relation to hatch date when nesting was earlier (prediction 2). Our rationale for prediction 1 was that the need to complete molt before fall migration is exacerbated when nesting is delayed. Prediction 2 is suggested by the advantage of restoring nutrients depleted during nesting before initiating molt. We tested predictions by assessing patterns of ninth-primary length in relation to number of days posthatch, modal hatch date, and relative hatch date within years. We calculated molt initiation dates using parameter estimates from the best-supported model, using lengths and growth rates of ninth primaries. We estimated that Black Brant initiated molt an average of 14.5-19.5 days posthatch, depending on year. For modal hatch dates before 22 June (summer solstice), date of mean initiation of molt was negatively correlated with modal hatch date (b = -0.56), whereas for modal hatch dates after 22 June, mean initiation of molt began an average of 16.1 days after hatch. In years when modal hatch date was before 22 June, Black Brant waited longer after their clutches hatched before beginning molt, which suggests an advantage of greater stored nutrient levels before initiating molt. By contrast, in late-nesting years, Black Brant began molt 16 days after they hatched their clutches, which suggests that (1) a minimum average period posthatch was required before molt commenced and (2) there was a cost of further delay in molt in late-nesting years. Declining photoperiod following the summer solstice is a reasonable candidate for the signal that Black Brant use to initiate molt in late-nesting years. Ritmo de Muda de las Remeras en Hembras Adultas de Branta bernicla nigricansResumen.-El ritmo de la muda es un rasgo crítico de la historia de vida porque la muda es un proceso nutricionalmente demandante que debe ser completado antes de la migración de otoño. Usamos datos desde 1992 a 2008 para evaluar las hipótesis de que la iniciación de la muda pre-básica de Branta bernicla nigricans está controlada de manera última por (1) la necesidad de completar la muda antes de la migración de otoño y (2) las ventajas de recuperar las reservas de nutrientes antes del crecimiento de las plumas. Específicamente, esperábamos que la muda ocurriera poco después de la eclosión en años en que la anidación fue retardada (predicción 1), pero esperábamos que los individuos retrasaran la muda en relación con la fecha de eclosión cuando la anidación sucedió t...

Plasticity in moult speed and timing in an arctic‐nesting goose species

“…dates. Interestingly, once we corrected for the variability in moult speed due to the moult stage, the average delay of 16 d between hatching and moult initiation estimated in greater snow geese was identical to the value reported by Singer et al (2012) in black brants moulting in Alaska. Therefore, this makes us confident that our estimates of moult initiation dates were credible in our study.…”

“…Moult was initiated on average 16 d (range: 8 to 18 d) after the median hatching date (8 July). Inter-annual variability of moult initiation date (coefficient of variation CV  2.5%) was higher than for laying or hatching dates (CV  2.1 and 1.6%, respectively) but similar to moult completion the interval between hatching and moulting, as previously found in black brant in Alaska (Singer et al 2012). Conversely, we showed that moult initiation date was directly related to previous reproductive events and to the timing of snow-melt, a dominant factor governing nest initiation date in greater snow geese (Dickey et al 2008).…”

“…Results from those studies and from Singer et al (2012) suggest that, after hatching, females need time to recover a suffi cient body condition to initiate their fl ight feather moult. Low body condition may also be a source of stress, which could have repercussions on feather quality (De La Hera et al 2009, DesRochers et al 2009).…”

“…Timing of moult initiation was found to be partially dependent on nesting phenology (Singer et al 2012). A minimum of 16 d was required between hatching and moult initiation, leading to a delay in moult initiation during late nesting years.…”

“…Considering that previous studies in the black brant found little variation in the speed of feather growth (Taylor 1995, Singer et al 2012, we expected that possible adjustments in moult phenology in response to environmental conditions should be primarily governed by change in the timing of moult initiation. We hypothesized that the timing of moult should be less flexible than the timing of breeding due to the constraint of regaining flight capabilities before the onset of the fall migration.…”