Yellow-eyed penguins Megadyptes antipodes seemingly forage at discrete marine locations over the continental shelf, where they are believed to feed predominantly at the seafloor. Such behaviour would distinguish them from most other penguin species that generally employ pelagic foraging strategies. From 2003 to 2005 we studied the foraging behaviour of yellow-eyed penguins breeding near Oamaru, New Zealand. We used 2 types of data loggers: GPS loggers recorded geographical position and dive depth at set intervals, while time-depth recorders (TDRs) recorded only dive depth. The penguins performed day trips (range: 12 to 20 km from the coast) or shorter evening trips (range: < 7 km). Consecutive foraging trips of individuals revealed remarkably consistent foraging routes. Birds travelled along similar -at times congruent -paths, markedly changed course at distinct locations, and revisited certain locations on separate trips, indicating skilful navigation. Three trip stages could be distinguished on one-day trips. During the outgoing (seaward travelling) and incoming (shoreward travelling) stages the birds followed linear courses. These stages were separated by a period of midday activity in which birds exhibited higher dive effort and often tended to stay within confined areas. The diving behaviour revealed an exclusive bottom-foraging strategy, with 87% of all dives being benthic dives; the majority of non-benthic dives occurred during the last 2 to 3 h of the trip, indicating primarily travelling behaviour. Furthermore, yellow-eyed penguins employ benthic dives not only when feeding but also frequently when travelling. We suggest that benthic dives might facilitate navigation and, consequently, account for the consistent foraging patterns of yellow-eyed penguins.
BackgroundForaging efficiency determines whether animals will be able to raise healthy broods, maintain their own condition, avoid predators and ultimately increase their fitness. Using accelerometers and GPS loggers, features of the habitat and the way animals deal with variable conditions can be translated into energetic costs of movement, which, in turn, can be translated to energy landscapes.We investigated energy landscapes in Gentoo Penguins Pygoscelis papua from two colonies at New Island, Falkland/Malvinas Islands.ResultsIn our study, the marine areas used by the penguins, parameters of dive depth and the proportion of pelagic and benthic dives varied both between years and colonies. As a consequence, the energy landscapes also varied between the years, and we discuss how this was related to differences in food availability, which were also reflected in differences in carbon and nitrogen stable isotope values and isotopic niche metrics. In the second year, the energy landscape was characterized by lower foraging costs per energy gain, and breeding success was also higher in this year. Additionally, an area around three South American Fur Seal Arctocephalus australis colonies was never used.ConclusionsThese results confirm that energy landscapes vary in time and that the seabirds forage in areas of the energy landscapes that result in minimized energetic costs. Thus, our results support the view of energy landscapes and fear of predation as mechanisms underlying animal foraging behaviour. Furthermore, we show that energy landscapes are useful in linking energy gain and variable energy costs of foraging to breeding success.Electronic supplementary materialThe online version of this article (doi:10.1186/s12983-017-0219-8) contains supplementary material, which is available to authorized users.
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.
Free-ranging marine predators rarely search for prey along straight lines because dynamic ocean processes usually require complex search strategies. If linear movement patterns occur they are usually associated with travelling events or migratory behaviour. However, recent fine scale tracking of flying seabirds has revealed straight-line movements while birds followed fishing vessels. Unlike flying seabirds, penguins are not known to target and follow fishing vessels. Yet yellow-eyed penguins from New Zealand often exhibit directed movement patterns while searching for prey at the seafloor, a behaviour that seems to contradict common movement ecology theories. While deploying GPS dive loggers on yellow-eyed penguins from the Otago Peninsula we found that the birds frequently followed straight lines for several kilometres with little horizontal deviation. In several cases individuals swam up and down the same line, while some of the lines were followed by more than one individual. Using a remote operated vehicle (ROV) we found a highly visible furrow on the seafloor most likely caused by an otter board of a demersal fish trawl, which ran in a straight line exactly matching the trajectory of a recent line identified from penguin tracks. We noted high abundances of benthic scavengers associated with fisheries-related bottom disturbance. While our data demonstrate the acute way-finding capabilities of benthic foraging yellow-eyed penguins, they also highlight how hidden cascading effects of coastal fisheries may alter behaviour and potentially even population dynamics of marine predators, an often overlooked fact in the examination of fisheries’ impacts.
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