Record phenological responses to climate change in three sympatric penguin species

1. The timing of breeding is an important aspect of any species' realised niche, reflecting adaptations to synchronise with food supplies, dilute predation, avoid competition and exploit seasonal fluctuations in resources. Breeding phenology is typically studied either through long-term monitoring of focal populations (limiting the strength of inferences about species-wide traits and trends) or, when conducted at a landscape level, using remotely visible traits (restricting most studies to plants). 2. For the first time, this study demonstrates landscape-scale measurement of vertebrate breeding phenology using a network of 77 time-lapse cameras to monitor three sympatric penguin species across 37 colonies in the Antarctic Peninsula and Sub-Antarctic islands. 3. Camera temperature loggers showed penguin colony locations are warming up four times faster (0.3°C/year) than the continental average (0.07°C/year), already the second fastest-warming area in the world. 4. We analysed the start of the breeding season of Adélie, Chinstrap and Gentoo penguins at a sub-continental scale between 2012 and 2022. The phenology of all three species advanced at record rates (10.2 ± 2, 10.4 ± 1.5 and 13 ± 4 days/decade, respectively). 5. Different demographic trends as well as intra- and inter-species differences in response to environmental change suggest niche-based response differences between species. 6. Phenological advances are causing niche separation to reduce. In this context, the Gentoo penguins' generalist and resident nature seems better suited to compete for space and resources than krill-specialist Chinstraps and ice-specialist Adélies. 7. Synthesis: A decade of observation of the three pygoscelid penguins shows they are advancing their settlement phenology at record speeds in relation to climate change across the Antarctic Peninsula. These changes are species-dependent, reflecting different vulnerabilities and opportunities depending on their niche and life-history traits. In the long term, the trend towards earlier settlement risks increasing inter-species competition, causing trophic and temporal mismatch, and reshaping community assemblages.

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