Heterogeneity in the intrinsic quality and nutritional condition of
individuals affects reproductive success and consequently fitness.
Understanding differences in energy allocation towards survival and
reproduction within and among years might help explain variability in
individual 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 provide evidence for relationships between
breeding probability and clutch size (posterior mean of β = 0.45, 95%
CRI = 0.33 – 0.57, SD = 0.06), breeding probability and nest initiation
date (posterior mean of β = -0.12, 95% CRI = -0.2 ¬– -0.04, SD =
0.04), and an interaction between clutch size and initiation date
(posterior mean of β = -0.12, 95% CRI = -0.2 – -0.04, SD = 0.04).
Average lifetime clutch size also had a weak positive relationship with
survival probability (posterior mean of β = 0.03, 95% CRI = -0.01 –
0.7, SD = 0.02). Our results support the use of demographic buffering
strategies for black brant; reductions in reproductive energy allocation
preserve high adult survival rates during years with poor environmental
conditions, maximizing future reproductive value. We also indirectly
show links among environmental conditions during growth, fitness, and
energy allocation, highlighting the effects of early growth conditions
on individual heterogeneity, and subsequently, reproductive investment.