Acoustic characterization of the three-dimensional prey field of foraging chinstrap penguins (original) (raw)
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Testing optimal foraging theory in a penguin-krill system
Proceedings of the Royal Society B: Biological Sciences, 2014
Food is heterogeneously distributed in nature, and understanding how animals search for and exploit food patches is a fundamental challenge in ecology. The classic marginal value theorem (MVT) formulates optimal patch residence time in response to patch quality. The MVT was generally proved in controlled animal experiments; however, owing to the technical difficulties in recording foraging behaviour in the wild, it has been inadequately examined in natural predator–prey systems, especially those in the three-dimensional marine environment. Using animal-borne accelerometers and video cameras, we collected a rare dataset in which the behaviour of a marine predator (penguin) was recorded simultaneously with the capture timings of mobile, patchily distributed prey (krill). We provide qualitative support for the MVT by showing that (i) krill capture rate diminished with time in each dive, as assumed in the MVT, and (ii) dive duration (or patch residence time, controlled for dive depth) i...
Marine Ecology Progress Series, 2013
Interspecific competition is an important structuring element in marine ecosystems, especially in the Southern Ocean which offers few prey choices to comparatively large predator populations. We present the first simultaneous observations of at-sea behaviour and attendance patterns of 3 synchronously breeding, central place, krill foragers at Bouvetøya-a small, isolated, sub-Antarctic island in the South Atlantic. Time depth recorders and satellite transmitters were deployed during the austral summer of 2007/2008 on 47 lactating Antarctic fur seals Arctocephalus gazella (AFS) rearing pups and on 20 macaroni Eudyptes chrysolophus (MAC) and 30 chinstrap Pygoscelis antarctica penguins (CHIN) rearing chicks. All 3 species showed a strong preference for the west side of the island, and their foraging ranges overlapped markedly. Solar elevation influenced the timing of departures from, and arrivals to, the island with markedly different patterns between the seals and the penguins. Diving patterns also showed significant differences among the 3 species, with the frequency of diving being higher at night for the AFS, while both penguin species dove more frequently during the day. But a common, vertical diel pattern occurred in all 3 species, with shallow diving occurring at night and deep diving during the day, consistent with the vertical migration of krill. MACs targeted 2 depth layers for feeding, including a deep prey layer at ~70 m, which was not exploited by AFSs and CHINs. The results suggest that there is potential for competitive overlap among these 3 krill predators at Bouvetøya, but that it is reduced via both spatial (horizontal and vertical) and temporal partitioning of foraging areas.
Preliminary investigations of prey pursuit and capture by king penguins at sea
2000
Prey pursuit and capture by king penguins (Aptenodytes patagonicus) were investigated with multiple data recorders in the Crozet Archipelago during the 1995/96 austral summer. Birds were fi tted with a swim speed and depth data logger that sampled every second making possible fi ne-scale analyses of underwater behavior. Data were obtained for two birds for periods of 2. 5 and 2. 9 days, respectively. During each dive deeper than 30 m, the swimming speed was constant at around 2 m/s, defi ned as "cruising" speed. However, steep acceleration events ("dashes") were observed. These dashes occurred in "U", "W" and "Plateau" shaped dives. Based on their shape, these dashes were separated into "Rushes" (28 % of all dash events) where penguins moved upward and increased their speed from the cruising speed; "Adjusts" (59 %) where penguins swam also upward and increased their speed to return to cruising speed after a short slowdown , and "Intermediates" (13 %) which were "Adjusts" events that briefly overshot the cruising speed. "Rushes" mainly occurred at the bottom phase of deep dives. They were followed by other dash events in 80% of cases. Moreover, "Rushes" lasted longer and the distance traveled during them was bigger compared to other dash events. "Adjusts" events were observed at the bottom phase and early part of the ascent phase. They were single events within a dive in 50% of cases. These results suggested that dashes, especially "Rushes" may be the main pursuit and capturing behavior performed by king penguins on patchily distributed preys in water deeper than 100m.
PLoS ONE, 2013
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.
Marine Biology, 2003
A new concept based on analysis of dive depth data was developed to help estimate prey consumption in ten free-ranging Magellanic penguins (Spheniscus magellanicus) that were brooding chicks. By simultaneously analysing the undulations in the dive depth profile (measured by time-depth recorders, TDRs) and beak opening (obtained from the recently developed intra-mandibular angle sensors, IMASEN), it was possible to determine the proportions of the undulations in the dive profile that resulted (or not) in prey capture. This methodology allowed the number of prey consumed to be estimated with a mean error of 10±6% using TDR data alone. If the mean mass of prey is known, then the overall mass of prey consumed per unit time can be determined. Additionally, the method allows estimation of the depth at which prey is taken and thus indicates how penguins exploit the water column. Due to its simplicity, the proposed methodology has applications for other Spheniscus penguin species and should be considered for other marine endotherm divers that show undulations in the dive depth profile.
Diving behaviour and prey of the Humboldt Penguin (Spheniscus humboldti)
Journal of Ornithology, 1989
Underwater diving by volant seabirds is almost invariably concerned with foraging. Measurement of the dive duration can help elucidate underwater behaviour of seabirds; dive times positively correlated with depth indicate that the birds may be feeding on the bottom (e.g. DEWAR 1924) whereas dive times not correlated with depth, or very short in relation to depth, indicate that the birds are probably swimming near the surface or in mid-water regions (eg. SrECFRI~D et al. 1975).
Scientific Reports, 2019
Discovering the predictors of foraging locations can be challenging, and is often the critical missing piece for interpreting the ecological significance of observed movement patterns of predators. This is especially true in dynamic coastal marine systems, where planktonic food resources are diffuse and must be either physically or biologically concentrated to support upper trophic levels. In the Western Antarctic Peninsula, recent climate change has created new foraging sympatry between Adélie (Pygoscelis adeliae) and gentoo (P. papua) penguins in a known biological hotspot near Palmer Deep canyon. We used this recent sympatry as an opportunity to investigate how dynamic local oceanographic features affect aspects of the foraging ecology of these two species. Simulated particle trajectories from measured surface currents were used to investigate the co-occurrence of convergent ocean features and penguin foraging locations. Adélie penguin diving activity was restricted to the upper mixed layer, while gentoo penguins often foraged much deeper than the mixed layer, suggesting that Adélie penguins may be more responsive to dynamic surface convergent features compared to gentoo penguins. We found that, despite large differences in diving and foraging behavior, both shallow-diving Adélie and deeper-diving gentoo penguins strongly selected for surface convergent features. Furthermore, there was no difference in selectivity for shallow-versus deep-diving gentoo penguins. Our results suggest that these two mesopredators are selecting surface convergent features, however, how these surface signals are related to subsurface prey fields is unknown.
Foraging strategies and prey encounter rate of free-ranging Little Penguins
Marine Biology, 2006
There is little information on the effort put into foraging by seabirds, even though it is fundamental to many issues in behavioural ecology. Recent researchers have used changes in the underwater cruising speed of penguins to allude to prey ingestion since accelerations are thought to reflect the encounter and pursuit of prey.