Opposite, but insufficient, phenological responses to climate in two circumpolar seabirds: Relative roles of phenotypic plasticity and selection

1. The magnitude of climate change has been greatest in the Arctic, accelerating climate-induced shifts in phenology, but wildlife responses vary. Variation may be due to the relative importance of phenotypic plasticity or phenotypic selection. 2. Here, we examine and contrast the environmental drivers of plasticity in breeding phenology of two circumpolar seabirds at their receding summer range limit using unique datasets of marked individuals covering 25 and 30years. Based on prior knowledge of the local ecosystems, we predicted that climate would generate opposing patterns of plasticity in the two populations. 3. Laying phenology of kittiwakes in the Gulf of Alaska was associated with a large-scale climate oscillation (Pacific Decadal Oscillation) while the Arctic-breeding murres adjusted laying to sea-ice conditions. Kittiwakes laid earlier after experiencing colder climate about 2 years prior and laying dates did not advance over the study, but murres laid earlier when warmer climate led to earlier spring seaice break-up, and murre laying dates advanced by 1 week since 1990. Selection favoured earlier laying in both species. 4. Both populations adjusted breeding phenology to environmental variation, but we anticipate opposing effects on phenology with continued climate change. Ice-constrained species can likely adapt to some extent because plasticity can provide the necessary shift to this physical barrier, although individuals were only able to adjust by similar to 1 week while ice conditions advanced by over a month. In more temperate regions, where phenology is driven by bottom-up effects, plasticity and selection counteract one another leading to limited adaptability. We provide insights into the likely adjustments by Arctic marine animals to an increasingly warmer and ice-less summer.

Automated summary

The magnitude of climate change and wildlife responses in the Arctic vary due to the relative importance of phenotypic plasticity or phenotypic selection. This study examines and contrasts the environmental drivers of plasticity in breeding phenology of two circumpolar seabirds and predicts opposing patterns of plasticity based on local ecosystems. The findings suggest that both populations adjust breeding phenology to environmental variation, but the effects on phenology with continued climate change may be different.