Diel diving behavior of breeding gentoo penguins on King George Island in Antarctica

Many marine birds dive to catch prey in water. The gentoo penguin (Pygoscelis papua), a specialized diving seabird that preys on krill and fish, is distributed from the sub-Antarctic islands to Antarctic regions. Here, we observed the diving behavior of breeding gentoo penguins on King George Island, South Shetland Islands, Antarctica. Using a time–depth recorder, we collected diving depths every second from seven gentoo breeders for 5–21 days during the chick-rearing period and analyzed their diving characteristics. Most dives occurred in shallow water, although the dive efficiency (=bottom duration time/[dive duration + post-dive surface time]) was highest at depths of 30–35 m and decreased as the penguins dove deeper. Gentoo penguins did not dive more frequently during the day than at night, but during nighttime, most dives occurred in shallow water (<20 m) and the dive efficiency was also higher at this time. As penguins repeated their foraging trips, the number of dives, depth of dives, and trip duration did not change significantly. Our results suggest that the diel dive patterns of gentoo penguins might be related to the vertical migration of krill (upward to the surface at night). In addition, we observed that gentoo penguins could perform active diving behavior even at night, possibly aided by civil twilight during the chick-rearing period in Antarctic regions.多数海鸟会潜入水中捕猎。巴布亚企鹅（Pygoscelis papua）是一类特化的潜水海鸟，以磷虾和鱼类为食，其分布范围从亚南极岛屿延伸至南极地区。本研究于南极南设得兰群岛的乔治王岛，对繁殖期的巴布亚企鹅的潜水行为进行了观测。本研究使用时间深度记录仪（Time-depth recorder），在育雏期对7只繁殖期巴布亚企鹅进行了为期5至21天的观测，每秒采集一次潜水深度数据，并分析了它们的潜水特征。尽管潜水效率（=底部持续时长/[潜水时长+潜水后水面停留时长]）在30至35米的深度时达到峰值，并随着企鹅下潜深度增加而下降，但多数潜水都发生在浅水环境中。巴布亚企鹅的日间潜水频率并未高于夜间，但夜间的多数潜水都发生在20米以内的浅水区，且此时的潜水效率也更高。随着企鹅反复开展觅食行程，其潜水次数、潜水深度以及觅食行程时长均未出现显著变化。本研究结果表明，巴布亚企鹅的昼夜潜水模式可能与磷虾的垂直迁徙有关（夜间磷虾会向上移动至海面）。此外，本研究还观测到，巴布亚企鹅甚至可在夜间进行主动潜水行为，这可能得益于南极地区育雏期的民用暮光环境。