The role of conspecifics during pelagic foraging of Magellanic and benthic foraging of Gentoo penguins in the Beagle Channel, Argentina

Harris, Sabrina; Pütz, Klemens; Mattern, Thomas; Scioscia, Gabriela; Rey, Andrea Raya

doi:10.1007/s00227-022-04163-3

Cited by 4 publications

(3 citation statements)

References 67 publications

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“…Giant petrels are not known to cooperate when they forage; where there is evidence of sociality in foraging seabirds generally, it is typically in the following of conspecifics to prey patches (e.g., Jones et al., 2018 ) and perhaps attacking prey schools simultaneously (e.g., Harris et al., 2023 ). Many giant petrels will congregate to consume a single carcass, however.…”

Section: Discussionmentioning

confidence: 99%

A fearful scourge to the penguin colonies: Southern giant petrel (Macronectes giganteus) predation on living Magellanic penguins (Spheniscus magellanicus) may be more common than assumed

Wagner,

Rebstock,

Boersma

2024

Ecology and Evolution

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Southern giant petrels (Macronectes giganteus) are important consumers that range across the oceans throughout the southern hemisphere. In Argentina, previous studies have shown they eat primarily pinnipeds and penguins, which they are assumed to scavenge, although there are occasional anecdotes of them attacking living penguins. Here we describe a predation attempt by a trio of southern giant petrels on a molting adult Magellanic penguin (Spheniscus magellanicus) at the large colony at Punta Tombo, Argentina. We relate giant petrel attendance patterns at the colony to the penguins' phenology, showing how giant petrel numbers rise with the increasing prevalence of vulnerable penguins. We suggest that living penguins—both fledglings and adults—may constitute a more seasonally significant proportion of the giant petrel diet than previously assumed, and their capture may represent a specialized predation technique.

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Section: Discussionmentioning

confidence: 99%

A fearful scourge to the penguin colonies: Southern giant petrel (Macronectes giganteus) predation on living Magellanic penguins (Spheniscus magellanicus) may be more common than assumed

Wagner,

Rebstock,

Boersma

2024

Ecology and Evolution

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“…This trophic shift may be due to a diet shift as individuals are likely to have fed on a higher proportion of lower trophic level squat lobster ( Munida gregaria ) than higher level Fuegian sprat ( Sprattus fuegensis ) in the former year and increased the proportion of Fuegian sprat the following season. Squat lobster may be easier to obtain as individuals remain suspended in the water column and do not attempt to flee like Fuegian sprat (see video footage in Harris et al, 2023 ), and therefore stress levels modulated by foraging effort of breeding individuals was lower that season. It is important to keep in mind that all sampled individuals in the current study were able to raise at least one chick to fledging, therefore endured the challenges of the given breeding season successfully.…”

Section: Discussionmentioning

confidence: 99%

The influence of tourist visitation on the heterophyl to lymphocyte ratios and trophic values of Magellanic penguins (Spheniscus magellanicus) at Martillo Island, Argentina

Harris,

Scioscia,

Raya Rey

2023

Conservation Physiology

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Wildlife tourism is increasing worldwide and monitoring the impact of tourism on wild populations is of the utmost importance for species conservation. The Magellanic penguin Spheniscus magellanicus colony at Martillo Island, Argentina, was studied in the 2016–2020 breeding seasons. In all seasons, adults and chicks belonged to: (i) an area close to or within the tourist trail or (ii) an area far from the tourist trail and out of sight of the tourists. Blood samples were taken for carbon and nitrogen stable isotope composition, in order to estimate trophic niches, and for smears that were made in situ and were then stained in the laboratory where leucocyte counts and differentiation were made under optical microscope. Heterophil to lymphocyte ratios were used as proxies of stress. Repeated sampling showed individual stress levels reduced while wintering. In 2017, stress levels and trophic values were lower than 2018 for the same individuals. Trophic levels did not differ between tourism and no tourism areas within each season, and differed between 2017 and the remaining seasons, indicating a possible diet shift that year. Stress levels were higher for the tourism area than the no tourism area for adults and chicks in all years except for 2020, when stress levels in the tourism area were lower and similar to the no tourism area that year and previous years. Vessel transit within the Beagle Channel and tourist visitation to the penguin colony was greatly reduced in 2020 due to the Covid-19 pandemic. A combination of internal characteristics and external factors may be affecting the stress physiology of individuals. Therefore, future research should include sampling of multiple aspects of penguin physiology, behaviour and environmental context in order to evaluate each effect on Magellanic penguin stress and, ultimately, inform the conservation of this iconic species in time.

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“…Accelerometers mounted on the head or jaw [ 11 – 13 ], ingested stomach temperature probes [ 14 ], and movement data [ 15 ], (but see [ 16 ]) have been used to estimate feeding rates. Direct observation of predation events, prey, and foraging habitats have been done for large animals such as seals [ 17 – 20 ] and whales [ 21 – 25 ], but assessing predator responses to changes in prey availability remains difficult in the marine environment, particularly for smaller animals such as penguins [ 26 – 30 ]. While there are studies that have observed penguins striking at prey [ 12 , 31 , 32 ], in this work we quantify the prey field and prey availability, which may influence feeding behaviors and success.…”

Section: Introductionmentioning

confidence: 99%

A method to estimate prey density from single-camera images: A case study with chinstrap penguins and Antarctic krill

Hermanson,

Cutter,

Hinke

et al. 2024

PLoS ONE

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Estimating the densities of marine prey observed in animal-borne video loggers when encountered by foraging predators represents an important challenge for understanding predator-prey interactions in the marine environment. We used video images collected during the foraging trip of one chinstrap penguin (Pygoscelis antarcticus) from Cape Shirreff, Livingston Island, Antarctica to develop a novel approach for estimating the density of Antarctic krill (Euphausia superba) encountered during foraging activities. Using the open-source Video and Image Analytics for a Marine Environment (VIAME), we trained a neural network model to identify video frames containing krill. Our image classifier has an overall accuracy of 73%, with a positive predictive value of 83% for prediction of frames containing krill. We then developed a method to estimate the volume of water imaged, thus the density (N·m-3) of krill, in the 2-dimensional images. The method is based on the maximum range from the camera where krill remain visibly resolvable and assumes that mean krill length is known, and that the distribution of orientation angles of krill is uniform. From 1,932 images identified as containing krill, we manually identified a subset of 124 images from across the video record that contained resolvable and unresolvable krill necessary to estimate the resolvable range and imaged volume for the video sensor. Krill swarm density encountered by the penguins ranged from 2 to 307 krill·m-3 and mean density of krill was 48 krill·m-3 (sd = 61 krill·m-3). Mean krill biomass density was 25 g·m-3. Our frame-level image classifier model and krill density estimation method provide a new approach to efficiently process video-logger data and estimate krill density from 2D imagery, providing key information on prey aggregations that may affect predator foraging performance. The approach should be directly applicable to other marine predators feeding on aggregations of prey.

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The role of conspecifics during pelagic foraging of Magellanic and benthic foraging of Gentoo penguins in the Beagle Channel, Argentina

Cited by 4 publications

References 67 publications

A fearful scourge to the penguin colonies: Southern giant petrel (Macronectes giganteus) predation on living Magellanic penguins (Spheniscus magellanicus) may be more common than assumed

A fearful scourge to the penguin colonies: Southern giant petrel (Macronectes giganteus) predation on living Magellanic penguins (Spheniscus magellanicus) may be more common than assumed

The influence of tourist visitation on the heterophyl to lymphocyte ratios and trophic values of Magellanic penguins (Spheniscus magellanicus) at Martillo Island, Argentina

A method to estimate prey density from single-camera images: A case study with chinstrap penguins and Antarctic krill

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