Population trends and breeding success variability of Adélie penguins, a bioindicator of Antarctic environments, have been attributed to changing sea-ice extents; however, causative mechanisms remain unclear. By electronically tagging 175 penguins in four seasons with contrasting sea-ice conditions, we show that ice-free environments enhance, not deteriorate, foraging efficiencies and breeding success. In an ice-free season, penguins traveled by swimming rather than walking, leading to larger foraging areas, shorter trip durations, and lower energy expenditure than three ice-covered seasons. Freed from the need to find cracks for breathing, dive durations decreased, and more krill were captured per unit dive time, which may also be associated with phytoplankton blooms and increased krill density in the sunlit ice-free water. Consequently, adult body mass, chick growth rates, and breeding success increased. Our findings explain the regional population trends and demonstrate a key link among sea ice, foraging behavior, and reproductive success in this iconic species.

阿德利企鹅（南极环境的生物指标）的种群趋势和繁殖成功率的变化归因于海冰范围的变化；然而，致病机制仍不清楚。通过在四个季节用不同的海冰条件对 175 只企鹅进行电子标记，我们表明无冰环境提高而不是恶化，觅食效率和繁殖成功。在无冰季节，企鹅通过游泳而不是步行旅行，与三个冰雪季节相比，它们的觅食区域更大，行程时间更短，能量消耗更低。无需寻找裂缝进行呼吸，潜水时间减少，单位潜水时间捕获更多磷虾，这也可能与浮游植物大量繁殖和在阳光照射的无冰水中增加磷虾密度有关。最后，成年体重、雏鸡生长速度和繁殖成功率都有所提高。我们的研究结果解释了区域种群趋势，并证明了这一标志性物种的海冰、觅食行为和繁殖成功之间的关键联系。