The Interplay of Ecological Opportunity and Adult Foraging Strategies in Juvenile Sparrow Individual Specialization

Temporal variation in resource availability, amplified by global change, may have strong impacts on species breeding at temperate and high latitudes that cue their reproduction to exploit seasonal resource pulses. This study examines how resource availability (ecological opportunity) and parental care influence niche partitioning between and within age classes in the rufous-collared sparrow, which provides extensive parental care. We hypothesized juveniles would exhibit narrower niches focused on high-quality resources compared to adults, regardless of ecological opportunity. We used stable isotope analysis to quantify individual and population niches in juveniles and adults across the breeding season in two cohorts experiencing contrasting resource landscapes. Contrary to our initial hypothesis, juveniles exhibited greater individual specialization and smaller total niche widths during periods when resource availability was high in comparison to periods of low ecological opportunity. Interestingly, niche characteristics of adults remained stable across seasons despite a shift in trophic level, highlighting their potential role in providing a consistent diet for their young. These findings reveal a dynamic interplay between ecological opportunity, parental care, and individual specialization, with important implications for understanding population resilience under variable resource scenarios. The study also suggests that adult sparrows adapt their provisioning strategies based on ecological opportunity, potentially buffering offspring from environmental fluctuations. Understanding age-specific responses to resource variation is crucial for predicting species responses to ecological conditions, particularly in regions like central Chile where seasonal resource limitation is expected to become more variable in response to climate change.