A male yellow-eyed penguin from Boulder Beach on the Otago Peninsula, recently became a video star for researchers Thomas Mattern, Michael McPherson, Ursula Ellenberg, Yolanda van Heezik and Philipp Seddon, who were investigating the use of high definition video loggers to study marine wildlife.
Even the scientists were surprised by how much they could learn about the foraging behaviour of yellow-eyed penguins at sea.
It’s important, because one of the biggest challenges the penguins face right now is finding enough food to raise their chicks in the breeding season.
“We developed a camera logger that records full HD video through a wide-angle lens, providing high resolution footage with a greater field of view than other camera loggers. The main goal was to assess the suitability of this type of camera for the analysis of various aspects of the foraging ecology of a marine predator, the yellow-eyed penguin in New Zealand. However, the deployment revealed far more information than was anticipated.”
“The video data provided novel insights into physiological aspects of the penguin’s diving activities and allowed us to draw conclusions about prey capture techniques. In this paper, we summarise our findings, demonstrate analytical approaches to evaluate animal-borne video data, and highlight the multi-disciplinary potential of wide-angle, full HD video loggers.”
The yellow-eyed penguin is known to forage on the sea floor and to feed primarily on demersal fish species that live and feed on or near the bottom of the sea. This may make them vulnerable to changes in their marine environment.
“Degradation of seafloor ecosystems in the wake of commercial bottom fisheries are suspected to influence yellow-eyed penguin foraging success and population developments. While the species’ at-sea movement and diving behaviour have been subject to a number of studies in the past decades, information about their benthic habitat is very limited.”
Yellow-eyed penguins are classified as ‘Endangered’ by the IUCN Redlist and are found on the sub-Antarctic Auckland and Campbell Islands as well as the south-eastern coastlines of New Zealand’s South Island and Stewart Island, including the Otago Peninsula.
“This study was carried out at the Boulder Beach complex, Otago Peninsula. Penguins from this site have been subject to foraging studies that have suggested substantial impact of bottom trawling activities on the yellow-eyed penguins’ at-sea movements. The video logger was deployed on a breeding male yellow-eyed penguin tending two chicks on 17 December 2015. The bird left on a single foraging trip on 18 December before the device was recovered on 19 December; the penguin continued to breed normally after the deployment.”
The day following camera deployment, the penguin performed a 10.7 hour-long foraging trip.
“The first dive event was recorded at 5:30 hrs and the last event concluded at 16:10 hrs. The bird performed 286 dives of which 159 dive profiles matched the criteria for benthic (sea floor) dives. Median dive depth reached during benthic dives was 54.4 m (range: 4.8–62.1 m, n = 159) whereas the majority of pelagic (open ocean water column) dives occurred in the upper 10 m of the water column (median: 7.8 m, range: 0.5–31.7 m, n = 127); camera footage confirmed these to be principally travelling behaviour.”
“For the first 3.5 h of the foraging trip (05:30–09:00 hrs) the bird performed mainly pelagic dives, indicating primarily travelling behaviour towards its main foraging grounds; yellow-eyed penguins are known to exhibit high individual site fidelity with regards to foraging locations. Between 09:00 and 16:00 hrs the bird principally devoted it’s time to benthic diving while shallow dives dominated the remaining 10 min of the foraging trip.”
The chosen male penguin turned out to be quite a successful forager and predator. Frame-by-frame analysis allowed accurate timing of prey pursuits and time spent over certain seafloor types.
“A total of 20 prey pursuits were recorded at the seafloor. Fourteen of these resulted in successful capture of either opalfish (Hemerocoetes monopterygius, 10 specimens) or blue cod (Parapercis colias, 2 specimens); prey species could not be identified during two captures, but the penguin’s searching behaviour and ease of ingestion suggested these were opalfish.”
“All of these prey pursuits occurred at the sea floor with the penguin swimming very close to the bottom. During the camera operation time, the penguin spent 5.7 min on prey pursuit, which corresponds to 19% of the total time the bird foraged along the seafloor (29.9 min) and 6% of its total dive time (89.9 min). The penguin spent most of its active prey pursuit on opalfish (total 3.8 min, 12 events), 0.7 min were used to capture blue cod (2 events), and 1.2 min of prey pursuit did not result in successful prey capture.”
Video footage showed that prey species were associated with certain seafloor types, revealed different predator evasion strategies by opalfish and blue cod, and highlighted varying energetic consequences for penguins pursuing certain types of prey.
“When catching opalfish, the penguin would glide closely above the seafloor, sometimes briefly accelerating before starting to hover over a certain spot while repeatedly pecking at the substrate until the prey item was captured. During encounters with blue cod prolonged pursuits ensued during which fish zigzagged at a fast pace along the seafloor. In one instance the fish was caught as it appeared to seek shelter at the base of a horse mussel protruding from the substrate.”
Prey encounters were associated with certain sea floor habitat types.
“All prey encounters occurred over coarse sand although the sediment structure differed depending on prey species. Opalfish were principally encountered on sediment ripples (93.6% of the total prey pursuit time, while flat bottom habitat played a more important role during blue cod pursuits (52.8% of blue cod pursuit time.”
“Other aspects that could be analysed were the timing of breathing intervals between dives and observe exhalation events during prey pursuits, a previously undescribed behaviour. Screen overlays facilitated analysis of flipper angles and beat frequencies throughout various stages of the dive cycle.”
“Flipper movement analysis confirmed decreasing effort during descent phases as the bird gained depth, and that ascent was principally passive. Breathing episodes between dives were short (<1 second) while the majority of the time was devoted to subsurface scanning with a submerged head.”
So why do yellow-eyed penguins forage so close to the sea floor? The researchers believe the technique could serve several purposes.
“It could be a strategy to flush out benthic prey that blends in with the substrate, but it could also mean the penguin has a greater chance to see its prey from the side, and thus reduce the effect of prey camouflage. Opalfish, for example, are very well camouflaged and very difficult to make out from above. This species seems to principally rely on its camouflage as means of predator avoidance since none of the opalfish captures involved a chase.”
Blue cod rely on a totally different defence – agility and speed.
“In contrast, during both successful blue cod encounters, extended high-speed chases ensued before the fish was ultimately captured. Blue cod and opalfish differ significantly in their anatomy with the small, slender opalfish presumably lacking the physical prowess for prolonged swimming when compared to muscular blue cod. When facing an air breathing predator, the latter strategy is likely advantageous as the predator’s increased energy requirements for pursuit make escape a more likely outcome for the prey. The penguin’s hasty ascent and subsequent failure to consume a blue cod it captured after a 22-second-long chase demonstrates the efficacy of this evasion strategy.”
Opalfish and blue cod are among the most important prey items in the yellow-eyed penguin’s diet.
“While both fish species have comparable energetic values, the body mass of opalfish is considerably lower when compared to blue cod. It is possible that the energy gain from catching blue cod justifies the expenditure to catch it, while the easier-to-catch opalfish might need to be caught in larger quantities. However, recent studies suggest that blue cod might be suboptimal prey for chick-rearing yellow-eyed penguins due to their size so that the penguin’s ability to locate prey such as opalfish might be a decisive factor with regards to reproductive success.”
Video loggers can help to determine how much fisheries are affecting penguin foraging grounds.
“The outer ranges of the marine habitat of yellow-eyed penguins from the Otago Peninsula is subject to bottom fisheries which have a profound effect on benthic ecosystems. Yellow-eyed penguins have been found to forage in the wake of trawl fisheries, potentially to the detriment of their reproductive success. Changes in sediment structure and epibenthic biodiversity as a result of bottom trawl disturbance likely negatively affect the penguins’ foraging success. Camera loggers can help to determine how much of the penguins’ foraging habitat has been compromised by fishing activities and what the consequences are for this species’ foraging behaviour and success.”
In future studies, deploying video loggers on penguins could enable detailed mapping of the benthic habitat within the species’ home ranges.
“Yellow-eyed penguins are known to have preferred individual foraging areas often with little overlap between birds. Moreover, the birds tend to often dive along the seafloor when swimming towards their foraging grounds so that camera logger data in combination with GPS information can be used to establish spatial biodiversity indices and benthic habitat maps.”
There are still limitations to the use of camera loggers, however, such as battery life and the amount of memory needed to store high definition video data.
“In our case, 15 minutes of footage resulted in video file sizes of 1.5 gigabytes. Moreover, the deployment with the camera set-up we used requires a certain amount of predictability, particularly knowledge about how soon after departure the bird is likely to engage in behaviours that are of interest (e.g., prey pursuit). For all these reasons, the technology currently available is best suited for short-term deployments on central place foragers.”
The full research report is published online in PeerJ and is freely available to download.