Migration is a key life-history strategy that allows animals to exploit seasonal food peaks while avoiding periods of scarcity. The success of a migratory strategy hinges on the balance between reproductive output and survival. Long-lived species, such as Arctic-breeding geese, can trade off survival and reproductive success by skipping breeding in years when conditions for reproduction are unfavourable. Breeding propensity — the likelihood of mature females breeding in a given year — therefore plays a crucial role in population dynamics.
We studied how spring conditions (onset of spring) affect breeding propensity and nesting success of barnacle geese (Branta leucopsis) breeding along a latitudinal gradient. We collated tracking data of barnacle geese breeding from the temperate region in the Netherlands, to Novaya Zemlya in the high Arctic. By using a novel technique to derive breeding attempts from high-resolution tracking data, our study avoids the bias introduced by overlooking non-breeding birds, providing a comprehensive understanding of breeding dynamics across the entire breeding range.
The results revealed that breeding propensity is significantly influenced by spring phenology in Arctic regions. At latitudes >66° N, breeding propensity decreased markedly in late springs compared to early springs. Nesting success, mirrored the pattern of breeding propensity, declining in later springs at Arctic latitudes. However, temperate latitudes exhibit consistently high breeding propensity and nesting success, seemingly unaffected by spring phenology. The relationship between breeding propensity and spring phenology at Arctic latitudes aligns with the idea that local food availability and conditions upon arrival play a crucial role. At temperate latitudes, food and nesting site availability is usually not limited by snow cover, and timing of spring might therefore be less important. Furthermore, agricultural intensification provides a stable and nutrient-rich food supply which could facilitate high breeding propensity regardless of spring phenology.
Earlier Arctic springs, driven by climate warming, have mostly been considered to have negative impacts on reproductive success through phenological mismatches. However, our study suggests that higher breeding propensity and nesting success in early springs may partially offset these negative impacts. This underscores the intricate relationship between spring phenology and reproductive success in Arctic breeding geese and other species. As climate change continues to influence spring timing, understanding these relationships becomes crucial for assessing the broader implications on population viability.
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Reference: Boom, M. P., Schreven, K. H., Buitendijk, N. H., Moonen, S., Nolet, B. A., Eichhorn, G., van der Jeugd, H.P. & Lameris, T. K. (2023). Earlier springs increase goose breeding propensity and nesting success at Arctic but not at temperate latitudes. Journal of Animal Ecology. Early view
Text and photo credit: Michiel Boom,Dutch Centre for Avian Migration and Demography (NIOO-KNAW)