Exploration during early life: distribution, habitat and orientation preferences in juvenile king penguins

BACKGROUND

The early life of marine apex predators is poorly known, particularly for diving species. The orientation and foraging skills are presumably less developed in juveniles than in adults, especially during their first year at sea when juveniles might disperse further than adults.

METHODS

Over two years of monitoring, we tracked the movements of 17 juvenile king penguins (Aptenodytes patagonicus, ~ 1 year old) using satellite relay tags from Crozet Archipelago (Southern Indian Ocean), starting when birds left their natal colony for the first time. For comparison we also tagged 6 non-breeding adults, which at that stage, similar to juveniles, are unhampered by reproductive constraints and might roam further than breeders. We used a combination of cluster analysis and habitat modelling to investigate and compare the movement patterns and habitat use of experienced (non-breeding adults) and non-experienced (juveniles) individuals.

RESULTS

While juvenile penguins and non-breeding adults followed similar routes, the movements by adults started later in the season and ranged over a considerably smaller area than juveniles. Net squared displacement analysis revealed that both groups did not move to a specific wintering area. Changes in direction of juveniles in respect to their departure island were similar and synchronous for both years. Habitat models revealed that foraging behaviour was affected by environmental variables such as wind or current speeds, sea surface temperature, or oceanic productivity, for both stages. Analysis of tracks revealed that birds moved predominately perpendicular or against the main direction of the Antarctic Circumpolar Current and the prevailing wind during austral summer (juveniles only) and autumn (juveniles and non-breeding adults). However, both juveniles and adults were more likely to move against the prevailing winds if productivity increased along their trajectories.

CONCLUSIONS

The exceptional duration of our tracking study provided unprecedented insights into the distribution, habitat preferences and orientation of two poorly known life history stages of an expert avian diver. Our study suggests that juveniles might use both innate and learnt skills to reach profitable foraging areas during their first year at sea, which is critical in long-lived species.

Where do penguins go during the inter-breeding period? Using geolocation to track the winter dispersion of the macaroni penguin

Although penguins are key marine predators from the Southern Ocean, their migratory behaviour during the inter-nesting period remains widely unknown. Here, we report for the first time, to our knowledge, the winter foraging movements and feeding habits of a penguin species by using geolocation sensors fitted on penguins with a new attachment method. We focused on the macaroni penguin Eudyptes chrysolophus at Kerguelen, the single largest consumer of marine prey among all seabirds. Overall, macaroni penguins performed very long winter trips, remaining at sea during approximately six months within the limits of the Southern Ocean. They departed from Kerguelen in an eastward direction and distributed widely, over more than 3.10(6) km(2). The penguins spent most of their time in a previously unrecognized foraging area, i.e. a narrow latitudinal band (47-49 degrees S) within the central Indian Ocean (70-110 degrees E), corresponding oceanographically to the Polar Frontal Zone. There, their blood isotopic niche indicated that macaroni penguins preyed mainly upon crustaceans, but not on Antarctic krill Euphausia superba, which does not occur at these northern latitudes. Such winter information is a crucial step for a better integrative approach for the conservation of this species whose world population is known to be declining.

Feeding behaviour of free-ranging penguins determined by oesophageal temperature

Sea birds play a major role in marine food webs, and it is important to determine when and how much they feed at sea. A major advance has been made by using the drop in stomach temperature after ingestion of ectothermic prey. This method is less sensitive when birds eat small prey or when the stomach is full. Moreover, in diving birds, independently of food ingestion, there are fluctuations in the lower abdominal temperature during the dives. Using oesophageal temperature, we present here a new method for detecting the timing of prey ingestion in free-ranging sea birds, and, to our knowledge, report the first data obtained on king penguins (Aptenodytes patagonicus). In birds ashore, which were hand-fed 2-15 g pieces of fish, all meal ingestions were detected with a sensor in the upper oesophagus. Detection was poorer with sensors at increasing distances from the beak. At sea, slow temperature drops in the upper oesophagus and stomach characterized a diving effect per se. For the upper oesophagus only, abrupt temperature variations were superimposed, therefore indicating prey ingestions. We determined the depths at which these occurred. Combining the changes in oesophageal temperatures of marine predators with their diving pattern opens new perspectives for understanding their foraging strategy, and, after validation with concurrent applications of classical techniques of prey survey, for assessing the distribution of their prey.

Impact of externally attached loggers on the diving behaviour of the king penguin

The impact of relatively small externally attached time series recorders on some foraging parameters of seabirds was investigated during the austral summer of 1995 by monitoring the diving behaviour of 10 free-ranging king penguins (Aptenodytes patagonicus) over one foraging trip. Time-depth recorders were implanted in the abdominal cavities of the birds, and half of the animals also had dummy loggers attached on their backs. Although most of the diving behaviour was not significantly affected by the external loggers (P>0.05), the birds with externally attached loggers performed almost twice as many shallow dives, between 0 and 10 m depth, as the birds without external loggers. These shallow dives interrupted more frequently the deep-diving sequences in the case of birds with external loggers (percentage of deep dives followed by deep dives: 46% for birds with implants only vs. 26% for birds with an external attachment). Finally, the distribution pattern of the postdive durations plotted against the hour of the day was more heterogeneous for the birds with an external package. In addition, these penguins had extended surfacing times between two deep dives compared to birds without external attachments (P<0.0001). These results suggest the existence of an extra energy cost induced by externally attached loggers.

Seabirds as monitors of upper-ocean thermal structure. King penguins at the Antarctic polar front, east of Kerguelen sector

The main objective of this work was to assess the potential of diving birds to monitor the hydrographic features near the Antarctic polar front. We compared the temperature/depth profiles recorded by instrumented King penguins Aptenodytes patagonicus at Kerguelen Islands (South Indian Ocean) with the oceanographic and remote sensing (satellite) data available for the same area during the same season. The birds were equipped with time/depth/temperature recorders or Argos transmitters. In addition, two birds were instrumented (of which one successfully) both with a time/depth/temperature recorder and an Argos transmitter. King penguins foraged as far as 400 km from the coast, in water masses with a vertical temperature structure characteristic of the region just south of the polar front. The temperature/depth profiles recorded throughout the dives (up to 270 m) revealed a pronounced thermocline. A three-dimensional distribution of water temperature was reconstructed. Comparison with previous hydrographic data shows a high correlation. Instrumented predators may therefore usefully and cheaply complement the database provided by conventional hydrographic surveys and remote sensing, especially in distant and rough areas such as the Southern Ocean.

Diving energetics in king penguins (Aptenodytes patagonicus)

Dive duration in wild king penguins and the energetic cost of swimming in a 30m long swim channel were determined at Ile de la Possession, Crozet Archipelago, using external data loggers and respirometry, respectively. Calibrated electronic data loggers equipped with a pressure sensor were used to determine dive durations: 95% of dives were less than 6 min long and 66% of dives were less than 4 min long. Dive patterns show that king penguins may intersperse long dive durations (4-6.3 min) with short ones (1.5-3 min) and make surface pauses of variable duration between them (0.5-3.5 min), or dive regularly (for up to 5 h) with long dive durations (5 min) and constant interdive surface intervals (1.5 min). The latter indicates that the aerobic dive limits (ADL) of this species could be higher and oxygen consumption lower than previously reported. Assuming that king penguins dive within their aerobic limit, different approaches to the analysis of the data obtained in the swim channel are discussed to derive the ADL. Swimming speeds observed in the channel ranged from 0.9 to 3.4 m s-1. Transport costs were lowest between 1.8 and 2.2 m s-1. Although at 2.2 m s-1 king penguins used only 10.3 Wkg-1 over a dive+surface cycle (minimal transport costs of 4.7 J kg-1 m-1), we speculate that tisse oxygen consumption during submergence may be as low as 0.23 ml O2 kg-1 s-1 (2.1 times standard metabolic rate, SMR) or perhaps lower (which gives an ADL of 4.2 min). During surface phases, oxygen uptake would be increased to at least 1 ml O2kg-1 s-1 (9.3 times SMR). This implies that at least 70% of all dives are aerobic. Potential physiological mechanisms allowing king penguins to partition O2 consumption between submergence and surface periods remain, however, unclear.