Climate shifts are key drivers of ecosystem change. Despite the critical importance of Antarctica and the Southern Ocean for global climate, the extent of climate-driven ecological change in this region remains controversial. In particular, the biological effects of changing sea ice conditions are poorly understood. We hypothesize that rapid postglacial reductions in sea ice drove biological shifts across multiple widespread Southern Ocean species. We test for demographic shifts driven by climate events over recent millennia by analyzing population genomic datasets spanning 3 penguin genera (Eudyptes,Pygoscelis, andAptenodytes). Demographic analyses for multiple species (macaroni/royal, eastern rockhopper, Adélie, gentoo, king, and emperor) currently inhabiting southern coastlines affected by heavy sea ice conditions during the Last Glacial Maximum (LGM) yielded genetic signatures of near-simultaneous population expansions associated with postglacial warming. Populations of the ice-adapted emperor penguin are inferred to have expanded slightly earlier than those of species requiring ice-free terrain. These concerted high-latitude expansion events contrast with relatively stable or declining demographic histories inferred for 4 penguin species (northern rockhopper, western rockhopper, Fiordland crested, and Snares crested) that apparently persisted throughout the LGM in ice-free habitats. Limited genetic structure detected in all ice-affected species across the vast Southern Ocean may reflect both rapid postglacial colonization of subantarctic and Antarctic shores, in addition to recent genetic exchange among populations. Together, these analyses highlight dramatic, ecosystem-wide responses to past Southern Ocean climate change and suggest potential for further shifts as warming continues.

Worldwide, most crested penguin species (Eudyptes spp.) are in decline. New Zealand's subantarctic Antipodes Islands are of international significance for erect‐crested (Eudyptes sclateri) and rockhopper (Eudyptes filholi) penguins. Between 1995 and 2011, a 23% decline was recorded in the two penguin species on the Antipodes Islands. In October 2014, nest abundance counts on Antipodes Island were undertaken to determine if this decline was continuing, particularly in light of a significant storm event that hit the Antipodes area in January 2014 causing massive landslides during the penguin breeding season. All penguin colonies ground counted in 2011 were preferentially ground counted in 2014 or, if time or weather did not allow, were checked with binoculars to confirm colony presence or absence. Seventy‐three per cent of the colonies and the equivalent of 82% of all nests counted in 2011 were recounted in 2014. Overall, there was a 19% decline in erect‐crested penguin nests between 2011 and 2014. Rockhopper penguins showed a slight increase (2.6%). Landslides affected 11% of the main islands’ land area and 44% of surveyed nesting colonies. Erect‐crested penguin colonies with approximately 75% or greater of their area impacted by landslides showed a significantly greater decline than unaffected or only partially impacted colonies. Landslides showed a minimal effect on rockhopper nest numbers. There continues to be a significant decline of erect‐crested penguins at the Antipodes Islands. An increasing occurrence of extreme weather events are predicted with climate change and have the potential to increase land‐based flooding and landslides, adding additional impacts to terrestrial breeding marine species. Greater understanding of what is causing erect‐crested penguin decline is needed to prevent this endangered species from extinction.

New Zealand (NZ) is an internationally significant area for penguins. All NZ penguin species are listed in 'at risk' threat categories. The naturally uncommon Snares crested penguins (Eudyptes robustus), which are restricted to NZ subantarctic islands, are highly susceptible to localised stochastic events and human activities. There has been uncertainty about population size and trends for Snares crested penguins. We surveyed the nest abundance and distribution of Snares crested penguins on Northeast (NE) and Broughton Islands, Snares Island group, from late September to early October in 2008, 2010 and 2013 and compared results with a survey from 2000. Counts of all nests (nests with eggs and total observed nests) within all colonies around the islands were undertaken. In 2008, 19 845 ± 29 nests with eggs and 24 666 ± 38 total nests were counted from 111 colonies. In 2010, 25 525 ± 21 nests with eggs and 30 672 ± 26 total nests from 117 colonies were counted while in 2013, 25 149 ± 39 nests with eggs and 29 009 ± 45 total nests from 119 colonies were counted. Penguin nest numbers at the Snares appear to be stable overall when compared with the 2000 survey, which gave 28 396 nests with eggs (direct counts) and 30 607 total nests from 112 colonies. However, 2008 appears to be a year with considerably lower numbers of nests compared with other years. This apparently stable population is in contrast to most other crested penguins in the world. Given the extremely restricted distribution of Snares crested penguins and potential for a rapid catastrophic decline, we recommend surveys be continued at regular intervals in order to detect a significant decline and allow management measures to be implemented if needed.

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