King Penguin Chicks Research Articles

The current trajectory of king penguin (Aptenodytes patagonicus) chick numbers on Macquarie Island in relation to environmental conditions

Abstract Macquarie Island's king penguin (Aptenodytes patagonicus) population has changed dramatically over recent centuries. Following near decimation from commercial exploitation during the 19th and early 20th centuries, chick numbers increased rapidly from 1930–1980. Since then, the population's trajectory has remained unreported, and environmental factors potentially influencing the population are poorly understood. From 2007–2020, king penguin chicks were censused annually. Chick numbers fluctuated between years, ranging from 33,513–78,714. Overall, the numbers decreased at 1.06 ± 0.03% per annum. While further studies are required to infer causality, annual chick numbers were negatively correlated with environmental conditions on land and at sea. Heavy rainfall, total rainfall, and maximum east coast wave height during incubation correlated with fewer chicks that year. Warmer sea surface temperatures in the foraging region of adult king penguins during incubation and early chick-rearing also correlated with lower chick numbers. While interannual variability and the long generation time of king penguins makes it unclear if the decrease in chick numbers represent a decrease in the breeding population, it is clear the late 20th century rapid increase in Macquarie Island's breeding population has ceased. Ongoing monitoring will establish if this is indicative of the population stabilising or an ongoing population decline.

Increased mitochondrial energy efficiency in skeletal muscle after long-term fasting: its relevance to animal performance.

In the final stage of fasting, skeletal muscle mass and protein content drastically decrease when the maintenance of efficient locomotor activity becomes crucial for animals to reactivate feeding behaviour and survive a very long period of starvation. As mitochondrial metabolism represents the main physiological link between the endogenous energy store and animal performance, the aim of this study was to determine how a very long, natural period of fasting affected skeletal muscle mitochondrial bioenergetics in king penguin (Aptenodytes patagonicus) chicks. Rates of mitochondrial oxidative phosphorylation were measured in pectoralis permeabilized fibres and isolated mitochondria. Mitochondrial ATP synthesis efficiency and the activities of respiratory chain complexes were measured in mitochondria isolated from pectoralis muscle. Results from long-term (4-5 months) naturally fasted chicks were compared with those from short-term (10 day) fasted birds. The respiratory activities of muscle fibres and isolated mitochondria were reduced by 60% and 45%, respectively, on average in long-term fasted chicks compared with short-term fasted birds. Oxidative capacity and mitochondrial content of pectoralis muscle were lowered by long-term fasting. Bioenergetic analysis of pectoralis muscle also revealed that mitochondria were, on average, 25% more energy efficient in the final stage of fasting (4-5 months) than after 10 days of fasting (short-term fasted birds). These results suggest that the strong reduction in respiratory capacity of pectoralis muscle was partly alleviated by increased mitochondrial ATP synthesis efficiency. Such oxidative phosphorylation optimization can impact animal performance, e.g. the metabolic cost of locomotion or the foraging efficiency.

Breeding events of king penguin at the South Shetland Islands: Has it come to stay?

King penguins (Aptenodytes patagonicus) have a circum-subantarctic range though recently, pairs breeding in Antarctica were reported. In a scenario of environmental variability as it is recorded in Antarctic Peninsula and adjacent islands, one ecological response registered in penguins was the shift in its distribution and breeding range probably due to the increment in the areas available to breed and/or feed. In the 2014–2015 season, the first king penguin chick was registered at Stranger Point (62°S. 25 de Mayo/King George Island), which remained alive until 5 months old. This record represents the southernmost birth of this species and the fourth consecutive breeding attempts in this site. This provides further evidence of a possible consolidation of a new breeding site at South Shetland Islands and thus the southward expansion of the bio-geographic range. Moreover, it suggests that both terrestrial and marine environmental conditions were favourable for king penguins, at least until the beginning of the creche stage. Nevertheless, an increase in the number of breeding pairs is essential to ensure the survival of chicks and enable the colonization.

The effect of experienced individuals on navigation by king penguin chick pairs

Group members' individual experience can have important influences when navigating collectively. However, how exactly they structure group travel performance is still not fully understood. This study investigated how navigation and leadership dynamics are affected by the presence of an experienced individual in king penguin, Aptenodytes patagonicus, chick pairs. We tested pairs of chicks in which two partners differed in their level of prior navigational experience. Naïve pairs consisted of two chicks that had no previous homing experience. In mixed pairs, one chick was naïve, but the other chick had previous homing experience. Our results showed that in mixed pairs the navigational performance of naïve chicks improved if they travelled together with an experienced partner compared to when they walked alone. Experienced chicks, however, maintained their relatively high speeds and efficiencies irrespective of whether they walked with a partner or independently. We also observed a shift in leadership dynamics: in naïve pairs, both chicks took turns in leading and following, while in mixed pairs, experienced chicks tended to lead throughout. Our work provides a valuable empirical system in which to test theoretical models of leadership and information transfer within groups.

Resolution of navigational conflict in king penguin chicks

Conflicts may arise within a moving animal group if its members have different preferred destinations. Many theoretical models suggest that in maintaining group cohesion conflicting preferences can have an overwhelming influence on decision making. However, empirical studies, especially on wild animals, remain limited. Here, we introduce a new study system for investigating collective decision making: king penguins, Aptenodytes patagonicus. Their gregarious lifestyle, the colony's organization into subgroups and group travel make king penguins especially interesting for studying collective movements. Chicks spend their first year of life in groups with other chicks (creches), and if displaced will return to their creche. We examined how different levels of navigational conflict affect such homing, by comparing the performance of pairs of chicks from the same creche with pairs from different creches. The majority of chicks in both treatments travelled at least part of the journey together; when doing so they were more efficient and faster than individuals travelling alone. Chicks took turns in leading and following. Chicks with a common destination (same-creche pairs) were more precise at homing and less likely to split up than those with a conflict over preferred destinations (different-creche pairs). Our results support some, but not all, predictions derived from theoretical models.

Starting with a handicap: phenotypic differences between early‐ and late‐born king penguin chicks and their survival correlates

Summary The exceptionally long (c. 11 months) growth period of king penguin chicks (Aptenodytes patagonicus) is interrupted by the Austral winter. As a consequence, penguin chicks born late in the breeding season have little time to build‐up their energy reserves before the drastic energy bottleneck they experience during winter and face greater risks of mortality than early‐born chicks. Whereas it is well known that breeding adults alternate between early‐ and late‐breeding attempts, little is known on the phenotype of early‐ and late‐chicks, and on the potential existence of specific adaptive phenotypic responses in late‐born individuals. We investigated phenotypic differences between early‐ and late‐chicks and tested their survival correlates both before the winter and at fledgling. Chicks were sampled 10 days after hatching to measure body mass, plasma corticosterone levels, oxidative stress parameters and telomere length. Late‐chicks were heavier than early‐chicks at day 10. Late‐chicks also had higher corticosterone and oxidative stress levels, shorter telomere lengths and suffered from higher mortality rates than early‐chicks. For both early‐ and late‐chicks, high body mass close to hatching was a strong predictor of survival up to, and over, the winter period. In late but not early‐chicks, high corticosterone levels and long telomeres were significant predictors of survival up to winter and fledging, respectively. Our study provides evidence that late‐ and early‐king penguin chicks showed marked phenotypic differences 10 days after hatching. We provide an integrative discussion on whether these differences may be adaptive or not, and to what extent they may be driven by active maternal effects, indirectly induced by environmental effects, or stem from individual differences in parental quality.

Mitochondrial phenotypic flexibility enhances energy savings during winter fast in king penguin chicks.

Energy conservation is a key priority for organisms that live in environments with seasonal shortages in resource supplies or that spontaneously fast during their annual cycle. The aim of this study was to determine whether the high fasting endurance of winter-acclimatized king penguin chicks (Aptenodytes patagonicus) is associated with an adjustment of mitochondrial bioenergetics in pectoralis muscle, the largest skeletal muscle in penguins. The rates of mitochondrial oxygen consumption, and ATP synthesis and mitochondrial efficiency (ATP/O ratio) were measured in winter-acclimatized chicks. We used pyruvate/malate and palmitoyl-l-carnitine/malate as respiratory substrates and results from naturally fasted chicks were compared to experimentally re-fed chicks. Bioenergetics analysis of pectoralis muscle revealed that mitochondria are on average 15% more energy efficient in naturally fasted than in experimentally fed chicks, indicating that fasted birds consume less nutrients to sustain their energy-demanding processes. We also found that moderate reductions in temperature from 38°C to 30°C further increase by 23% the energy coupling efficiency at the level of mitochondria, suggesting that king penguin chicks realize additional energy savings while becoming hypothermic during winter. It has been calculated that this adjustment of mitochondrial efficiency in skeletal muscle may contribute to nearly 25% of fasting-induced reduction in mass-specific metabolic rate measured in vivo. The present study shows that the regulation of mitochondrial efficiency triggers the development of an economical management of resources, which would maximize the conservation of endogenous fuel stores by decreasing the cost of living in fasted winter-acclimatized king penguin chicks.

Metabolic response to lipid infusion in fasting winter-acclimatized king penguin chicks (Aptenodytes patagonicus)

During the cold austral winter, king penguin chicks are infrequently fed by their parents and thus experience severe nutritional deprivation under harsh environmental conditions. These energetic constraints lead to a range of energy sparing mechanisms balanced by the maintenance of efficient thermogenic processes. The present work investigated whether the high thermogenic capacities exhibited by winter-acclimatized king penguin chicks could be related to an increase in lipid substrate supply and oxidation in skeletal muscle, the main site of thermogenesis in birds. To test this hypothesis, we examined i) the effect of an experimental rise in plasma triglyceride on the whole metabolic rate in winter-acclimatized (WA) and de-acclimatized king penguin chicks kept at thermoneutrality (TN), and ii) investigated the fuel preference of muscle mitochondria. In vivo, a perfusion of a lipid emulsion induced a small 10% increase of metabolic rate in WA chicks but not in TN group. In vitro, the oxidation rate of muscle mitochondria respiring on lipid-derived substrate was +40% higher in WA chicks than in TN, while no differences were found between groups when mitochondria oxidized carbohydrate-derived substrate or succinate. Despite an enhanced fuel selection towards lipid oxidation in skeletal muscle, a rise of circulating lipids per se was not sufficient to fully unravel the thermogenic capacity of winter-acclimatized king penguin chicks.

The invisible cues that guide king penguin chicks home. The use of magnetic and acoustic cues during orientation and short-range navigation

King penguins (Aptenodytes patagonicus) live in large and densely populated colonies, where navigation can be challenging because of the presence of many conspecifics that could obstruct locally available cues. Our previous experiments demonstrated that visual cues were important but not essential for king penguin chicks' homing. The main objective of this study was to investigate the importance of non-visual cues, such as magnetic and acoustic cues, for chicks' orientation and short-range navigation. In a series of experiments, the chicks were individually displaced from the colony to an experimental arena where they were released under different conditions. In the magnetic experiments, a strong magnet was attached to the chicks' heads. Trials were conducted in daylight and at night to test the relative importance of visual and magnetic cues. Our results showed that when the geomagnetic field around the chicks was modified, their orientation in the arena and the overall ability to home was not affected. In a low sound experiment we limited the acoustic cues available to the chicks by putting ear pads over their ears, and in a loud sound experiment we provided additional acoustic cues by broadcasting colony sounds on the opposite side of the arena to the real colony. In the low sound experiment, the behavior of the chicks was not affected by the limited sound input. In the loud sound experiment, the chicks reacted strongly to the colony sound. These results suggest that king penguin chicks may use the sound of the colony while orienting towards their home.

Chick-provisioning strategies used by king penguins to adapt to a multiseasonal breeding cycle

Parental provisioning strategies are central to life history theory, as one of the main components that adults can adjust to maximize their fitness. In altricial species, newly born young rely entirely on parents for food. Provisioning strategies are thus crucial for offspring survival and growth, but they may also have major consequences for parental lifetime reproductive success, especially in long-lived species. We investigated provisioning strategies in an offshore seabird, the king penguin, Aptenodytes patagonicus , through the number of times parents return to the colony to feed their chick, using a pluriannual database on more than 800 microtagged penguins. King penguin chick rearing can be divided into three periods: (1) from thermal emancipation to the onset of winter, (2) winter and (3) from the end of winter to fledging. Overall, we found that the number of feeding visits was larger for males, as well as for older and larger individuals. The timing of the winter low-provisioning period (15 May–1 September; shorter than previously described) did not vary according to sex, age or breeding timing. We found four different parental strategies during the winter period, from complete absence to regular foraging trips, which led to different breeding success rates. These four strategies were observed in the 6 study years, and in both sexes, although in different proportions. They were not explained by individuals' age, and individuals were not consistent across years, the decision to follow a strategy probably reflecting the trade-off between the bird's current condition and its environment. ► Chick-provisioning strategies were investigated in 801 microtagged king penguins over 6 years. ► Chick rearing divided in three distinct invariant periods according to provisioning levels. ► During the low-provisioning winter period, adults exhibited four different strategies. ► Behavioural strategies may reflect bird condition/ocean resource trade-offs.

A mechanistic understanding of ageing revealed by studying the young

A main focus within biomedical research is to understand how adverse environmental conditions experienced during early development affects lifelong health (Barker 1992). Within this context, extensive research in rodent models and humans has shown that intrauterine growth retardation (IUGR) caused by nutrient restriction during early development is often followed by post-natal 'catch-up' growth when access to food resources improves. However, this accelerated growth rate seems to come at a cost, as metabolic and endocrine processes that are programmed during this time cause later-life onset of diseases such as obesity, insulin resistance and cardiovascular disease (reviewed in Crespi & Denver 2005). In this issue Molecular Ecology, Geiger et al. (2012) asked what are the costs of catch-up growth in nutrient-restricted king penguin chicks (Fig. 1) by measuring lengths of telomeres, the protective DNA sequences at the end of chromosomes, before and after catch-up growth, as the amount and rate of telomere sequence loss over time has been associated with reduced lifespan in both model and nonmodel organisms (see reviews of Costantini et al. 2010; Haussmann & Marchetto 2010). Geiger et al. (2011) found that chicks entering the post-winter growth season at a smaller size exhibited increased growth rates (i.e. catch-up growth) at the cost of increased oxidative stress and reduced telomere lengths compared with the chicks entering the growth period at a larger size. Furthermore, chicks that did not survive had drastically shorter telomere lengths and reduced antioxidant capacities at the beginning of the growth period than all other chicks, thereby directly associating telomere length to mortality. These results suggest that while catch-up growth allows smaller chicks to head off into the world on equal footing with chicks that hatched at a larger size, it likely comes at the cost of a shortened lifespan. Thus, this study provides a mechanism that supports the antagonistic pleiotropy theory of senescence (Promislow 2004).

Catching‐up but telomere loss: half‐opening the black box of growth and ageing trade‐off in wild king penguin chicks

One of the reasons for animals not to grow as fast as they potentially could is that fast growth has been shown to be associated with reduced lifespan. However, we are still lacking a clear description of the reality of growth-dependent modulation of ageing mechanisms in wild animals. Using the particular growth trajectory of small king penguin chicks naturally exhibiting higher-than-normal growth rate to compensate for the winter break, we tested whether oxidative stress and telomere shortening are related to growth trajectories. Plasma antioxidant defences, oxidative damage levels and telomere length were measured at the beginning and at the end of the post-winter growth period in three groups of chicks (small chicks, which either passed away or survived the growth period, and large chicks). Small chicks that died early during the growth period had the highest level of oxidative damage and the shortest telomere lengths prior to death. Here, we show that small chicks that grew faster did it at the detriment of body maintenance mechanisms as shown by (i) higher oxidative damage and (ii) accelerated telomere loss. Our study provides the first evidence for a mechanistic link between growth and ageing rates under natural conditions.

Heterothermy in growing king penguins

A drop in body temperature allows significant energy savings in endotherms, but facultative heterothermy is usually restricted to small animals. Here we report that king penguin chicks (Aptenodytes patagonicus), which are able to fast for up to 5 months in winter, undergo marked seasonal heterothermy during this period of general food scarcity and slow-down of growth. They also experience short-term heterothermy below 20 °C in the lower abdomen during the intense (re)feeding period in spring, induced by cold meals and adverse weather. The heterothermic response involves reductions in peripheral temperature, reductions in thermal core volume and temporal abandonment of high core temperature. Among climate variables, air temperature and wind speed show the strongest effect on body temperature, but their effect size depends on physiological state. The observed heterothermy is remarkable for such a large bird (10 kg before fasting), which may account for its unrivalled fasting capacity among birds.

Differential muscular myosin heavy chain expression of the pectoral and pelvic girdles during early growth in the king penguin (Aptenodytes patagonicus) chick

Continuous growth, associated with a steady parental food supply, is a general pattern in offspring development. So that young chicks can acquire their locomotor independence, this period is usually marked by a fast maturation of muscles, during which different myosin heavy chain (MyHC) isoforms are expressed. However, parental food provisioning may fluctuate seasonally, and offspring therefore face a challenge to ensure the necessary maturation of their tissues when energy is limited. To address this trade-off we investigated muscle maturation in both the pectoral and pelvic girdles of king penguin chicks. This species has an exceptionally long rearing period (1 year), which is prolonged when parental food provisioning is drastically reduced during the sub-Antarctic winter. Approximately 1 month post hatching, chicks acquire a functional pedestrian locomotion, which uses pelvic muscles, whereas swimming, which uses the pectoral muscles, only occurs 1 year later. We therefore tested the hypothesis that the MyHC content of the leg muscles reaches a mature state before those of the pectoral muscles. We found that leg muscle MyHC composition changed with the progressive acquisition of pedestrian locomotion, whereas pectoral muscle fibres reached their mature MyHC profile as early as hatching. Contrary to our predictions, the acquisition of the adult profile in pectoral muscles could be related to an early maturation of the contractile muscular proteins, presumably associated with early thermoregulatory capacities of chicks, necessary for survival in their cold environment. This differential maturation appears to reconcile both the locomotor and environmental constraints of king penguin chicks during growth.

Preparing to fledge: the adrenocortical and metabolic responses to stress in king penguin chicks

Summary 1. Modulating the adrenocortical response to stress and the corresponding mobilization of energy substrates allows animals to cope with energy‐demanding challenges imposed by ecological constraints. Whether such a modulation occurs during the fledging process of the king penguin chick (Aptenodytes patagonicus) was examined. In this seabird species, fledging is associated with moult completion, prolonged fasting and transition from terrestrial to marine life. 2. Specifically, it was tested whether the adrenocortical and metabolic responses to a capture‐handling stress i. depended on the developmental/moulting status of pre‐fledging birds, ii. were affected by their nutritional status, and iii. were inter‐related. 3. The adrenocortical response was 2–3 times lower at moult end and fledging than at the onset of moult, 1 month earlier. No direct evidence for a link between the adrenocortical response and moult‐related changes in circulating thyroid hormones was obtained. 4. At the onset of moult, chicks were in a nutritional status corresponding to phase I of fasting whereas those at moult end and fledging were in phase II of fasting. Thus, the adrenocortical response depended on nutritional status, being blunted during phase II when body proteins were spared and fat stores preferentially mobilized. 5. The metabolic response to acute stress was characterized by an increase in plasma glucose, NEFA and uric acid and by a decrease in plasma β‐hydroxybutyrate. Differences in this response between phase I and phase II fasting chicks suggest that the mix of energy substrates used to fuel energy demand during acute stress is the same as that routinely fuelling daily energy expenditure. We obtained no evidence for an interaction between corticosterone and metabolic responses. 6. Overall, the results suggest that, in pre‐fledging king penguin chicks, the nutritional rather than the developmental/moulting status modulates the adrenocortical and metabolic responses to an acute stress. The possible adaptive function of the blunting of these responses by the time of fledging is discussed.

Recent trends in numbers of four species of penguins at the Prince Edward Islands

Four species of penguin breed regularly at South Africa's Prince Edward Islands: king penguin Aptenodytes patagonicus, gentoo penguin Pygoscelis papua, macaroni penguin Eudyptes chrysolophus and southern rockhopper penguin E. chrysocome. In December 2008, it was estimated that some 65 000 pairs of king penguins were incubating eggs at Marion Island, the larger of the two islands in the group, and 2 000 pairs at Prince Edward Island. At Marion Island from 1987 to 2008, there was no long-term trend in numbers of king penguin chicks that survived to the end of the winter period, but there was considerable fluctuation in chick production in the 1990s. It was roughly estimated that on average 88% of king penguin chicks survived the winter period (from April to September/October). Numbers of gentoo penguins at Marion Island decreased from more than 1 300 pairs in the mid-1990s to fewer than 800 pairs in 2003, and then increased to almost 1 100 pairs in 2008 as breeding success improved. Between 1994/1995 and 2008/2009, numbers of macaroni and southern rockhopper penguins at Marion Island decreased by about 30% and 70% respectively. In 2008/2009, some 290 000 pairs of macaroni penguins bred at this island, mostly in two large colonies where there was a progressive decrease in the density of nests. At both these colonies, decreases in numbers breeding followed outbreaks of disease. Inadequate breeding success has influenced the decreases of macaroni and rockhopper penguins. In 2008/2009, some 42 000 pairs of southern rockhopper penguins bred at Marion Island and 12 000 pairs of macaroni penguins and 38 000 pairs of southern rockhopper penguins at Prince Edward Island.

State-dependent decisions during the fledging process of king penguin chicks

In birds, the chick's physical state at nest departure is critical for survival, especially for seabirds that shift from a terrestrial to a marine life. The timing of this life history transition should therefore be finely tuned by proximate factors reflecting the relative influence of parents and chicks. Using king penguins, Aptenodytes patagonicus , as a model, we investigated how food provisioning and chick developmental status and/or body condition interact with chick fledging behaviour to optimize the physical state at colony departure. During the month preceding colony departure, movements, developmental status and body condition were compared between naturally and experimentally fed chicks. Parents stopped feeding their moulting, obese chick on average 16 days before colony departure and no offspring anorexia was observed. All chicks left their feeding site at the time of moult end, indicating that complete feather development is a prerequisite for departing. The time between moult end and colony departure reduced both intra- and intergroup variation in body condition at departure, suggesting that this condition was optimized in terms of a trade-off between fat stores and buoyancy. After moult end, chicks increased their locomotor activity and energy expenditure, which contributes to the regulation of body condition. Our results indicate that the cessation of parental feeding does not trigger colony departure. Rather, the timing of departure depends on the chick's physical state, regardless of its recent feeding history. Thus, in king penguins, the parental decision to desert the chick seems to reflect a compromise between the offspring's body condition and its developmental status.

Transcriptional analysis of skeletal muscle adaptations to marine life in king penguin juveniles (Aptenodytes patagonicus)

King penguin chicks, that are strictly terrestrial during first year after hatching, must depart to sea to reach nutritional emancipation. Juvenile survival therefore depends on their adaptation to the energetic challenges of marine life: 1) harsh thermal environment, 2) long distant food resources, 3) repeated, deep and prolonged nutritional divings.To elucidate these adaptations, the transcriptome of pectoralis muscle, the main thermogenic and locomotor tissue, was analysed in juveniles that had never been to sea (n=4) and in naturally adapted juveniles (n=3) by using chicken Affymetrix DNA chips (Profilexpert, Lyon).Results showed the differential expression of nearly 3600 genes after marine life. Genes encoding enzymes of carbohydrate metabolism were down regulated while those encoding lipid transport and catabolism were up regulated suggesting an increased use of lipids as energy substrates. Further, transcripts encoding enzymes involved in cellular defense against reactive oxygen species and the associated injuries were also up regulated, suggesting an adaptive response against oxidative stress.This study opens large perspectives to elucidate how king penguins can survive in an energetically unfavorable and pro‐oxidative environment and what contributes to their remarkable longevity.This study received the financial support of the French Polar Institut (IPEV).

Orientation in a crowded environment: can King Penguin (Aptenodytes patagonicus) chicks find their crèches after a displacement?

For seabird species, the presence of conspecifics in a crowded breeding colony can obstruct locally available orientation cues. Thus, navigation to specific locations can present a challenging problem. We investigated short-range orientation in King Penguin (Aptenodytes patagonicus) chicks that live in a large and densely populated colony. The two main objectives were to determine whether chicks displaced to a novel location away from the colony (i) can orient towards the colony and return to their crèche and (ii) rely on visual or non-visual cues for orientation. To address these questions, a circular arena was constructed 100 m away from the colony. Chicks were released in the arena during the day and at night. After the orientation experiment in the arena, chicks were allowed to return to their home crèche, if they could. Our results showed that, during day trials, chicks preferred the half of the arena closer to the colony, but not at night. However, at night, birds spent more time on ;the colony half' of the arena if the wind blew from the colony direction. When animals were allowed to leave the arena, 98% of chicks homed during the day but only 62% of chicks homed at night. Chicks that homed at night also took longer to find their crèche. The experiments suggest that King Penguin chicks can find their crèche from a novel location. Visual cues are important for homing but, when visual cues are not present, animals are able to make use of other information carried by the wind.

Stomach stones in king penguin chicks

Many animals that possess a gizzard swallow stones or sandy grit, supposedly to aid in the mechanical breakdown of food. While this has been well documented in the literature, our study is the first to report the presence of stones in the gizzard of king penguin chicks. We found stones, so called ‘gastroliths’, in the pyloric region of the gizzard, the part of the digestive tract that is specialised for the mechanical breakdown of food. Stones were already present in the gizzard of chicks and, hence, during the first year of the life of king penguins, which is spent on land. Some chicks were found to have more than 130 stones (0.5–22 mm in size) in their gizzard. The gastroliths we found in king penguins are of the same geological origin as rocks present at the colony, which suggests that birds swallowed them there. The functional role of gastroliths in penguin chicks and adults is still unknown. We discuss the potential roles that these gastroliths might play in king penguins (i.e. aid in digestion, buoyancy control during foraging at sea, adaptation to fasting).