Heterogeneity in the intrinsic quality and nutritional condition of individuals affects reproductive success and consequently fitness. Black brant (Branta bernicla nigricans) are long-lived, migratory, specialist herbivores. Long migratory pathways and short summer breeding seasons constrain the time and energy available for reproduction, thus magnifying life-history trade-offs. These constraints, combined with long lifespans and trade-offs between current and future reproductive value, provide a model system to examine the role of individual heterogeneity in driving life-history strategies and individual heterogeneity in fitness. We used hierarchical Bayesian models to examine reproductive trade-offs, modeling the relationships between within-year measures of reproductive energy allocation and among-year demographic rates of individual females breeding on the Yukon-Kuskokwim Delta, Alaska using capture-recapture and reproductive data from 1988 to 2014. We generally found that annual survival tended to be buffered against variation in reproductive investment, while breeding probability varied considerably over the range of clutch size-laying date combinations. We provide evidence for relationships between breeding probability and clutch size, breeding probability and nest initiation date, and an interaction between clutch size and initiation date. Average lifetime clutch size also had a weak positive relationship with apparent survival probability. Our results support the use of demographic buffering strategies for black brant. These results also indirectly suggest associations among environmental conditions during growth, fitness, and energy allocation, highlighting the effects of early growth conditions on individual heterogeneity, and subsequently, lifetime reproductive investment.

We collected data at the Tutakoke River Colony (61.25◦N, 165.61◦W) and related brood rearing areas on the Yukon-Kuskokwim Delta near the mouth of the Kashunuk River from 1988-2014. May - June, nests were monitored every four days throughout nest initiation, and again before and during hatch. Observers recorded clutch sizes and initiation dates of nests during this time. Incubation time is generally 23-29 days, varying with laying date and clutch size. Thus, we back-calculated initiation dates for hatched nests using mean incubation period (~26 days). Mid-late July, adult and juvenile brant were herded into pens and marked with a unique U.S. Geological Survey metal band and an alpha-numerically coded plastic band during the adult wing-molt. Resighting occured throughout the breeding season (May-late July). We included capture-history data only for marked adult females (n = 7,845). We included data on mean lifetime clutch sizes for 6,256 individuals (µ = 3.83; SD = 1.129) and mean initiation dates for 5,207 individuals (µ = 146.45 (Julian Day); SD = 5.6). When clutch size or initiation date was unavailable for females included in the capture-history data, we filled out the clutch size and/or initiation date dataset row for those individuals with NAs.

Columns contain data for the years 1988-2014. Rows corresponding with the same individuals are the same across all datasets. Initiation dates are Julian dates.