Central place foragers select ocean surface convergent features despite differing foraging strategies (original) (raw)
Related papers
High sea surface temperatures driven by a strengthening current reduce foraging success by penguins
Scientific Reports, 2016
The world's oceans are undergoing rapid, regionally specific warming. Strengthening western boundary currents play a role in this phenomenon, with sea surface temperatures (SST) in their paths rising faster than the global average. To understand how dynamic oceanography influences food availability in these ocean warming "hotspots", we use a novel prey capture signature derived from accelerometry to understand how the warm East Australian Current shapes foraging success by a meso-predator, the little penguin. This seabird feeds on low trophic level species that are sensitive to environmental change. We found that in 2012, prey capture success by penguins was high when SST was low relative to the long-term mean. In 2013 prey capture success was low, coincident with an unusually strong penetration of warm water. Overall there was an optimal temperature range for prey capture around 19-21 °C, with lower success at both lower and higher temperatures, mirroring published relationships between commercial sardine catch and SST. Spatially, higher SSTs corresponded to a lower probability of penguins using an area, and lower prey capture success. These links between high SST and reduced prey capture success by penguins suggest negative implications for future resource availability in a system dominated by a strengthening western boundary current.
Linear tracks and restricted temperature ranges characterise penguin foraging pathways
Marine Ecology Progress Series, 2008
Marine predators are thought to follow sophisticated scale-dependent search strategies when seeking patchy and unpredictable prey. However, fine-scale information about these strategies has hitherto been difficult to obtain for diving predators that often remain at the sea surface for only limited periods of time. Using ARGOS telemetry and novel, low-powered, archival GPS, we followed the fine-scale at-sea behaviour of king penguins breeding on South Georgia. Results revealed that foraging pathways were generally linear, except at the finest scale, where movements probably reflected either fine-scale searching behaviour, or fine-scale random movements associated with having found prey. King penguins focused 45% of their foraging effort in waters with a specific surface temperature (5.0 to 5.5°C) -an environmental cue potentially important in helping them locate prey, thereby reducing their need to expend energy in area-restricted search patterns. Within these waters, penguins slowed down and increased their dive effort and degree of meandering. First Passage Time analysis revealed that penguins focused much of their effort at local scales, generally in areas with a radius of 2 km. In these areas, penguins dived marginally deeper and targeted waters that were significantly warmer at the bottom of their dives. Such information about fine-scale foraging behaviour will help increase our understanding of the environmental correlates that characterise areas where marine predators exploit their prey. The scale of these behavioural processes is better resolved using the fine-scale temporal and spatial resolution of GPS tracking data.
2010
Marine predators are thought to utilise oceanic features adjusting their foraging strategy in a scaledependent manner. Thus, they are thought to dynamically alter their foraging behaviour in response to environmental conditions encountered. In this study, we examined the foraging behaviour of King Penguins (Aptenodytes patagonicus) breeding at South Georgia in relation to predictable and stable oceanographic features. We studied penguins during their long post-laying foraging trips during December 2005 and January 2006. For this investigation, we undertook a simultaneous analysis of ARGOS satellite-tracking data and Mk 7 WildLife Computers Time Depth Recorder (TDR) dive data. To investigate correlations between foraging behaviour and oceanographic conditions, we used SST data from January 2006 from MODIS satellite AQUA. To determine changes in search effort, first passage time (FPT) was calculated; for analysis of dive behaviour, we used several dive parameters that are thought to be reliable indicators of changes in foraging behaviour. King Penguins appeared to target predictable mesoscale features in the Polar Front Zone (PFZ), either a warm-core eddy in the PFZ or regions of strong temperature gradients at oceanic fronts. Two different trip types could be distinguished: direct trips with a straight path to one foraging area at the edge of an eddy or at a thermal front, and circular trips where birds foraged along strong thermal gradients at the northern limit of the PFZ. It is likely that both trip types were a direct consequence of prey encounter rates and distributions, both of which are likely to be associated with these oceanographic features. Circular trips often included passages across the centre of an eddy where birds made deep foraging dives, but remained only a short time in the eddy, possibly because prey were too deep. All birds showed Area Restricted Search (ARS) at scales of <10 km. The two trip types had different ARS patterns, with clear ARS hotspots for direct trips and several ARS hotspots over the whole duration of the trip for circular trips. Dive behaviour had clear relationships with the changing water temperature and the time of day, presumably in response to different prey distribution. Especially for direct trips, dive behaviour showed significant differences within and outside of ARS hotspots. Thus, King Penguins appear to target predictable mesoscale features in the PFZ. They use ARS in different patterns to exploit the environment and adjust their foraging strategy and diving behaviour depending upon conditions they encountered. Diving behaviour showed correlations to ARS patterns, especially for direct trips, which may represent a favourable foraging strategy. The presence of predictable oceanic features allows King Penguins to focus their foraging effort, presumably allowing them to increase their foraging success and decrease their diving effort.
Adélie Penguin Foraging Location Predicted by Tidal Regime Switching
PLoS ONE, 2013
Penguin foraging and breeding success depend on broad-scale environmental and local-scale hydrographic features of their habitat. We investigated the effect of local tidal currents on a population of Adélie penguins on Humble Is., Antarctica. We used satellite-tagged penguins, an autonomous underwater vehicle, and historical tidal records to model of penguin foraging locations over ten seasons. The bearing of tidal currents did not oscillate daily, but rather between diurnal and semidiurnal tidal regimes. Adélie penguins foraging locations changed in response to tidal regime switching, and not to daily tidal patterns. The hydrography and foraging patterns of Adélie penguins during these switching tidal regimes suggest that they are responding to changing prey availability, as they are concentrated and dispersed in nearby Palmer Deep by variable tidal forcing on weekly timescales, providing a link between local currents and the ecology of this predator.
Deep Sea Research Part II: Topical Studies in Oceanography, 2011
In accord with the hypotheses driving the Southern Ocean Global Ocean Ecosystems Dynamics (SO GLOBEC) program, we tested the hypothesis that the winter foraging ecology of a major top predator in waters off the Western Antarctic Peninsula (WAP), the Adé lie penguin (Pygoscelis adeliae), is constrained by oceanographic features related to the physiography of the region. This hypothesis grew from the supposition that breeding colonies in the WAP during summer are located adjacent to areas of complex bathymetry where circulation and upwelling processes appear to ensure predictable food resources. Therefore, we tested the additional hypothesis that these areas continue to contribute to the foraging strategy of this species throughout the non-breeding winter season. We used satellite telemetry data collected as part of the SO GLOBEC program during the austral winters of 2001 and 2002 to characterize individual penguin foraging locations in relation to bathymetry, sea ice variability within the pack ice, and wind velocity and divergence (as a proxy for potential areas with cracks and leads). We also explored differences between males and females in core foraging area overlap. Ocean depth was the most influential variable in the determination of foraging location, with most birds focusing their effort on shallow (o 200 m) waters near land and on mixed-layer (200-500 m) waters near the edge of deep troughs. Within-ice variability and wind (as a proxy for potential areas with cracks and leads) were not found to be influential variables, which is likely because of the low resolution satellite imagery and model outputs that were available. Throughout the study period, all individuals maintained a core foraging area separated from other individuals with very little overlap. However, from a year with light sea ice to one with heavy ice cover (2001)(2002), we observed an increase in the overlap of individual female foraging areas with those of other birds, likely due to restricted access to the water column, reduced prey abundance, or higher prey concentration. Male birds maintained separate core foraging areas with the same small amount of overlap, showing no difference in overlap between the years. While complex bathymetry was an important physical variable influencing the Adé lie penguin's foraging, the analysis of sea ice data of a higher resolution than was available for this study may help elucidate the role of sea ice in affecting Adé lie penguin winter foraging behavior within the pack ice.
Marine Biology, 2010
Chinstrap, Pygoscelis antarctica, and gentoo, P. papua, penguins are sympatric species that inhabit the Antarctic Peninsula. To evaluate differences in the foraging habitat of these two species, we recorded their foraging locations and diving behavior using recently developed GPS-depth data loggers. The study was conducted on King George Island, Antarctica during the chick-guarding period of both species, from December 2006 to January 2007. The area used for foraging, estimated as the 95% kernel density of dive ([5 m) locations, overlapped partially between the two species (26.4 and 68.5% of the area overlapped for chinstrap and gentoo penguins, respectively). However, the core foraging area, estimated as the 50% kernel density, was mostly separate (12.8 and 25.0% of the area overlapped for chinstrap and gentoo penguins, respectively). Chinstrap penguins tended to use off-shelf (water depth [ 200 m) regions (77% of the locations for dives [5 m), whereas gentoo penguins mainly used on-shelf (water depth \ 200 m) areas (71% of dive locations). The data on foraging locations, diving behavior, and bathymetry indicated that gentoo penguins often performed benthic dives (28% of dives [5 m), whereas chinstrap penguins almost always used the epipelagic/mid-water layer (96% of dives [5 m). Diving parameters such as diving bottom duration or diving efficiency differed between the species, reflecting differences in the use of foraging habitat. The diving parameters also suggested that the on-shelf benthic layer was profitable foraging habitat for gentoo penguins. Conversely, the relationship between trip duration, date, and stomach content mass suggested that the chinstrap penguins went further from the colony to forage as the season progressed, possibly reflecting a reduction in prey availability near the colony. Our results suggest that chinstrap and gentoo penguins segregated their foraging habitat in the Antarctic coastal marine environment, possibly due to inter-and intra-specific competition for common prey resources. Communicated by S. Garthe.
Foraging patterns of polar penguins
Sub-antarctic and polar penguins have revealed important differences in the distances travelled to foraging areas, the physical and biological characteristics of foraging areas, and foraging patterns. Differences are associated with preferred prey and its abundance. Data were acquired using satellite transmitters and time/depth recorders, the former giving location and rates of travel, the latter diving depths and patterns. Distinctions between travel and feeding dives help to assess foraging success. Data were matched to satellite imagery for determination of sea surface conditions. Sub-antarctic penguins travel further than polar penguins, feed near the Antarctic polar front, and are primarily diurnal feeders. Polar species feed at edges of coastal ice, pack ice, and polynyas. Most locations are neritic. Adelies specialise in krill at shallow depth as do sub-polar Macaroni and Royal Penguins. Emperor Penguins target fish in the mesopelagic zone, which is true also of King Penguins feeding at the Antarctic Polar Front. Hunting with 24h of daylight, polar penguins feed continuously with little hourly variation in depth. Subantarctic penguins show considerable diet differences, with reduced feeding at night.
2012
""Marine top predators play a pivotal role in stabilizing marine food webs. Their presence is also a good bio-indicator of the state of our oceans making them invaluable tools for detecting changes in the marine environment. However, it is important to grasp a fundamental understanding of how predators integrate with their environment if we are to fully understand the link between top predators and lower trophic levels. Seabirds are top predators facing substantial threats from fisheries and climate change, thus understanding their ecology is of growing importance. Their life histories such as long life spans and late maturation have evolved as a means to cope with the heterogeneous ocean landscape and scarce prey availability. These birds have also evolved a suite of strategies to increase the probability of locating these scarce and patchy prey distributions. For instance, many seabirds, especially long ranged birds such as albatrosses and larger penguins, are hypothesized to utilize temperature gradients to locate meso-scale (100-1000 km) ocean physical features such as eddies, fronts and upwelling zones where nutrients are advected to the euphotic zone from deeper cool bottom waters. This nutrient injection drives productivity in the ocean making these features ideal feeding grounds for top predators. Seabirds are also capable of using olfactory cues and currents to locate these features. However on a fine to coarse scale (1-100 km) it is less understood how these predators locate patchy prey distributions where cues such as temperature may be ephemeral. African Penguins have short foraging ranges (10-50 km), and forage in dynamic coastal environments making them an ideal model for understanding how short-ranged top predators locate their prey. By modeling the sea-surface thermal habitat preferences, and the dive behavior in relation to thermoclines of African Penguins I assess how these short-ranged birds use ocean physical processes to increase the probability of locating their small pelagic prey. African Penguins breeding on Bird Island, Algoa Bay, were capable of utilizing temperature as a potential cue to foraging in three-dimensions. Penguins commuted east and south of their colony likely predicting the occurrence of cool nutrient rich waters from a periodic upwelling cell. Penguins departed in the early morning travelling towards these areas, maximizing the time they foraged during the day in cooler waters with a higher probability of containing prey patches. Penguins used a correlated random search strategy during foraging suggesting that these birds were continuously searching for prey, and it is therefore likely that penguins are limited by the patchy distribution of prey rather than a heterogeneous marine environment. When diving, penguins’ utilized thermoclines as either a potential cue to prey or by association, as their prey may be scattered around thermoclines. Penguins dived deeper foraging below the thermocline when the thermocline depth increased and also responded in their dive behaviour under different thermocline structures. For instance, when thermoclines were a diffuse barrier to nutrients and less likely to concentrate prey, birds dived deeper towards the benthos. Warm water intrusions into the bay from the Agulhas Current resulted in birds diving deeper in search of cooler bottom waters. This research also demonstrates the dual utility of bio-loggers as a method for generating accurate, high-resolution oceanographic data. These data can be used in future studies, generating a cross disciplinary platform for research. This thesis augments our knowledge base of the African Penguin. African Penguins show flexibility in their foraging behaviour by adjusting their dive behaviour to subsurface thermal structures. Penguins also demonstrated foraging optimization by using temperature cues and behavioral switching to maximize the probability of locating prey patches on a fine temporal and spatial scale. ""
Diving and foraging behaviour of Adélie penguins in areas with and without fast sea-ice
Polar Biology, 1997
The diving and foraging behaviours of Ade´lie penguins, Pygoscelis adeliae, rearing chicks at Hukuro Cove, Lu¨tzow-Holm Bay, where the fast sea-ice remained throughout summer, were compared to those of penguins at Magnetic Island, Prydz Bay, where the fast sea-ice disappeared in early January. Parent penguins at Hukuro Cove made shallower (7.1-11.3 m) but longer (90-111 s) dives than those at Magnetic Island (22.9 m and 62 s). Dive duration correlated with dive depth at both colonies (r"0.01&0.90), but the penguins at Hukuro Cove made longer dives for a given depth. Parents at Hukuro Cove made shorter foraging trips (8.1-14.4 h) with proportionally longer walking/swimming (diving (1 m) travel time (27-40% of trip duration) and returned with smaller meals (253-293 g) than those at Magnetic Island, which foraged on average for 57.2 h, spent 2% of time walking/swimming ((1 m) travel, and with meals averaging 525 g. Trip duration at both colonies correlated to the total time spent diving. Trip duration at Hukuro Cove, but not at Magnetic Island, increased as walking/swimming ((1 m) travel time increased. These differences in foraging behaviour between colonies probably reflected differences in sea-ice cover and the availability of foraging sites.
Progress in Oceanography, 2015
The open ocean is a highly variable environment where marine top predators are thought to require optimized foraging strategies to locate and capture prey. Mesoscale and sub-mesoscale features are known to effect planktonic organisms but the response of top predators to these features results from behavioural choices and is poorly understood. Here, we investigated a multi-year database of at-sea distribution and behaviour of female Southern elephant seals (Mirounga leonina) to identify their preference for specific structures within the intense eddy field of the dynamic Antarctic Circumpolar Current (ACC). We distinguished two behavioural modes, i.e. travelling and intensive foraging, using state-space modelling. We employed multisatellite Lagrangian diagnostics to describe properties of (sub-)mesoscale oceanic circulation. Statistical analyses (GAMMs and Student's t-tests) revealed relationships between elephant seal behaviour and (sub-)mesoscale features during the post-moulting period (January-August): travelling along thermal fronts and intensive foraging in cold and long-lived mesoscale water patches. A Lagrangian analysis suggests that these water patches -where the prey field likely developed and concentrated -corresponded to waters which have supported the bloom during spring. In contrast, no clear preference emerged at the (sub-)mesoscale during the post-breeding period (October-December), although seals were distributed within the Chlorophyll-rich water plume detaching from the plateau. We interpret this difference in terms of a seasonal change in the prey field. Our interdisciplinary approach contributes to elucidate the foraging strategies of top predators in a complex and dynamic environment. It also brings top down insights on prey distribution in remote areas where information on mid-trophic levels are strongly lacking and it identifies important physical-biological interactions relevant for ecosystem modelling and management.