Impact of predation on king penguin Aptenodytes patagonicus in Crozet Archipelago

Predation can have major effects on population dynamics, but predator–prey interactions in marine ecosystems have rarely been studied. While the king penguin is one of the most studied seabirds, little is known about the impact of predation on its population dynamics. Here, we determine the impact of the main predators (giant petrels and skuas) on king penguin breeding success taking into account the nocturnal predation of petrels. We found that predation is the most important source of breeding failure for king penguins. The smallest chicks within crèches are the most hunted. The periphery of the colony suffers the highest risk of predation during summer. Our study shows the unequal quality of some areas inside the colony in terms of predation risk and breeding success, and points out the importance of timing in successful breeding.     

Seasonal variation in the diet of the king penguin (Aptenodytes patagonicus) at sub-Antarctic Marion Island

King penguins are important consumers of marine resources, throughout the year, at the Prince Edward Islands. Meal size varied from 8.5–12.6% of adult mass, depending on the method of determination. In spite of the biases in the analysis favouring the overestimation of squid, fish and, in particular, myctophid fish accounted for the largest proportion of the stomach samples, 87% by wet mass, 75% by numbers and 69% by reconstituted mass. The relative abundance of fish in the diet dropped markedly in winter followed by a subsequent rise to nearly 100% in summer. This rise coincided with an increase in the chick growth rate and the king penguin population at the island and suggests the rise in relative abundance offish reflects a real increase in the availability of fish around the islands.
Juvenile and adult Krefftichthys anderssoni/Protomyctophum tenisoni and adult Electrona carlsbergi were the most common fish consumed. There was an increase in the modal size of K. anderssoni/P. tenisoni throughout the year which we interpret as growth of a single fish population. Juvenile Kondakoviu longimana was the important squid species taken by king penguins. Crustaceans were only rarely recorded in the diet and may have come from digestion of fish and squid stomachs.
This is the first study of the diet of a Southern Ocean pelagic predator that has identified myctophid fish as a major component of its diet. All three important fish species taken by king penguins at Marion Island have a wide distribution throughout the Southern Ocean and consequently may prove to be important dietary components of other Southern Ocean pelagic predators.     

Nocturnal predation of king penguins by giant petrels on the Crozet Islands

Dietary segregation of sympatric seabirds in the Southern Ocean is partly linked to differences in their foraging techniques. We have investigated the activity of giant petrels (Macronectes spp.) in a king penguin (Aptenodytes patagonicus) colony day and night during the austral winter of 2001 on the Crozet Islands. Using an automatic identification system and an infrared video camera, we followed 15 petrels tagged with micro transponders. Our data show that giant petrels predate king penguin chicks during the night. The activity of giant petrels is even slightly higher during nighttime than during the day. In addition, our data show a higher nocturnal activity by northern giant petrels (M. halli) than by southern giant petrels (M. giganteus). These unexpected results raise questions concerning visual adaptations to nocturnal foraging in giant petrels and their potential impact on the sleep, vigilance and crèching behavior of penguin chicks.     

Inter-annual variability in Chinstrap penguin diet at South Shetland and South Orkneys Islands

Inter-annual variability in the diet of Chinstrap penguins (Pygoscelis antarctica) at Laurie Island (South Orkney Islands) and 25 de Mayo/King George and Nelson Islands (South Shetland) was examined based on stomach contents of adults during the 2002/2003–2006/2007 and 2002/2003–2004/2005 breeding seasons, respectively. Krill (Euphausia superba) dominated the diet as frequency of occurrence (in 100% of samples), number (>99%), and percentage contribution in weight (>94.8%). Other prey items were minor and varied between years. The weight of stomach contents was significantly different. The percentage in weight of whole krill was used to compare the feeding conditions across seasons. It differed significantly at the three sites studied. Distribution of krill size varied among years and localities, showing different krill availability for penguins.     

Prevalence of Borrelia burgdorferi (the Lyme disease agent) antibodies in king penguin Aptenodytes patagonicus in Crozet Archipelago

The seabird tick Ixodes uriae (White) is common in subantarctic areas and is likely to be a vector of pathogenic agents. This paper reports on the prevalence of tick-infested adult king penguins (Aptenodytes patagonicus) and on antibodies to the Lyme disease agent (Borrelia burgdorferi sensu lato) in adult and chick penguins. Fifteen percent of the adults of the colony studied were tick infested. B. burgdorferi antibodies were detected in 14% of tick-infested adults' and in 6% of chicks' sera. The percentage of tick-infested adults differed significantly according to location in the colony, the highest density occurring on the upper slopes of the colony. The potential role of king penguins as B. burgdorferi reservoirs and the effect of this agent on king penguin populations remain unknown. The consequences for human health are discussed. Accepted: 15 March 1999     

Satellite remote sensing in monitoring change of seabirds: use of Spot Image in king penguin population increase at Ile aux Cochons,Crozet Archipelago

The king penguin colony at Ile aux Cochons, Crozet Archipelago (southern Indian Ocean) is the largest in the world. The change in its surface area was investigated by means of satellite remote sensing using spot scene. The satellite picture enabled us to locate the colony and to determine that the surface area occupied by the colony has increased by 56% between 1962 and 1988. The increase in the surface area occupied by the colony was confirmed by a map realised in 1982 (by the Institut Géographique National). The high resolution system available on the spot system which allows at present at 10 m ground resolution, and 5 m in the near future, can thus be a useful tool for monitoring medium to long-term changes in marine bird populations breeding in colonies composed of birds spaced a constant distance from one another. Based on the surface area occupied by the colony and the published data on the population size on Possession Island, as well as information on the breeding frequency of the species, we estimated that the total breeding population is about 1,000,000 pairs for the whole archipelago and that about 70% of birds breed at Ile aux Cochons.     

Projected poleward shift of king penguins' (Aptenodytes patagonicus) foraging range at the Crozet Islands, southern Indian Ocean

Seabird populations of the Southern Ocean have been responding to climate change for the last three decades and demographic models suggest that projected warming will cause dramatic population changes over the next century. Shift in species distribution is likely to be one of the major possible adaptations to changing environmental conditions. Habitat models based on a unique long-term tracking dataset of king penguin (Aptenodytes patagonicus) breeding on the Crozet Islands (southern Indian Ocean) revealed that despite a significant influence of primary productivity and mesoscale activity, sea surface temperature consistently drove penguins' foraging distribution. According to climate models of the Intergovernmental Panel on Climate Change (IPCC), the projected warming of surface waters would lead to a gradual southward shift of the more profitable foraging zones, ranging from 25 km per decade for the B1 IPCC scenario to 40 km per decade for the A1B and A2 scenarios. As a consequence, distances travelled by incubating and brooding birds to reach optimal foraging zones associated with the polar front would double by 2100. Such a shift is far beyond the usual foraging range of king penguins breeding and would negatively affect the Crozet population on the long term, unless penguins develop alternative foraging strategies.     

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).     

Cocktail-party effect in king penguin colonies

The king penguin, Aptenodytes patagonicus, breeds without a nest in colonies of several thousands of birds. To be fed, the chick must recognize the parents in a particularly noisy environment using only vocal cues. The call an adult makes when seeking the chick is emitted at a high amplitude level. Nevertheless, it is transmitted in a colonial context involving the noise generated by the colony and the screening effect of the bodies, both factors reducing the signal-to-noise ratio. In addition, the adult call is masked by a background noise with similar amplitude and spectral and temporal characteristics, enhancing the difficulty for the chick in finding its parents. We calculate that the maximum distance from the caller at which its signal can be differentiated from the background noise (signal-to-noise ratio equal to 1) should not exceed 8 to 9 m in a feeding area. But our tests show that, in fact, chicks can discriminate between the parental call and calls from other adults at a greater distance, even when call intensity is well below that of the noise of simultaneous calls produced by other adults. This capacity to perceive and extract the call of the parent from the ambient noise and particularly from the calls of other adults, termed the ''cocktail-party effect'' in speech intelligibility tests, enhances the chick''s ability to find its parents.     

The diet of the Southern rockhopper penguin Eudyptes chrysocome chrysocome at Beauchene Island, Falkland Islands

The diet of the Southern rockhopper penguin at Beauchene Island, Falkland Islands, was studied in the early chick-rearing period by quantitative analysis of adult stomach contents. Juvenile squid (Teuthowenia sp.) comprised on average 21% by numbers (c. 1000 per sample) and 53% by weight; crustaceans contributed 79% by numbers (c. 4000 per sample) but only 45% by weight, and fish 2% by weight. Of the crustaceans only the euphausids Euphausia lucens (66% by numbers), E. vallentini (19%) and Thysanoessa gregaria (15%) were present in significant quantities, and all are swarming species characteristic of the Patagonian shelf epipelagic zooplankton. Comparison is made with the limited dietary data available from other studies, and rockhopper penguins are suggested typically to feed opportunistically on swarming or shoaling zooplankton (particularly euphausids and young squid) and small fish. Whereas the average weight of the stomach contents was 220 g, the biomass of the individuals originally ingested was estimated to total 800 g; the c. 3000 kj this represents is consistent with the likely energy requirements of adults making daily foraging trips to rear small chicks.     

Contribution of alien and indigenous species to plant-community assemblages near penguin rookeries at Crozet archipelago

The influence of seabird colonies on a remote insular flora was investigated through the analysis of plant community patterns at the boundaries of three colonies of king penguins (Aptenodytes patagonicus) on the subantarctic Île de la Possession. This study revealed that the physical and chemical impacts of these seabirds greatly influence plant assemblages (community composition, alien and native species abundance and richness). Plant richness appears to be maximum for a moderate disturbance intensity, on areas slightly influenced by penguin activities. The abundance of alien species near penguin rookeries may be due to their ability to withstand animal-induced disturbances and to efficiently colonise the stripped areas. In addition, the diversity and abundance of alien species recorded in study plots depend on the location of the colony. The closer the colony is to the permanent scientific station, the higher the number and abundance of aliens recorded.     

Summer diet of king penguins (Aptenodytes patagonicus) at the Falkland Islands, southern Atlantic Ocean

The diet of king penguins (Aptenodytes patagonicus) brooding chicks was investigated during February 2001 at the Falkland Islands, where a small but increasing population is located at the limit of the breeding range of this species. Fish was the most important food source by number (98.0%) and reconstituted mass (97.8%), squids accounting for the remainder. Myctophid fishes represented the main part of the diet (97.7% by number and 96.6% by reconstituted mass), Protomyctophum choriodon being by far the main prey item (84.2% and 88.1%, respectively). Four other myctophids and one squid species each contributed to more than 1% of the diet by number: Krefftichthys anderssoni (4.8%), Electrona carlsbergi (4.6%), Gymnoscopelus nicholsi (2.2%) and Protomyctophum tenisoni (1.8%), together with small juveniles of Gonatus antarcticus (1.8%). Twelve squid species were identified from accumulated lower beaks, including the ommastrephid Martialia hyadesi (48.3% by number), the onychoteuthids Moroteuthis ingens (15.6%), Kondakovia longimana (10.5%) and Moroteuthis knipovitchi (7.3%), and Gonatus antarcticus (9.2%). The stable-carbon and stable-nitrogen isotopic composition of chick food and adult blood differed in a way that suggests that, during the same trip, adult birds fed for themselves in distant foraging grounds, and fed for their chicks on their way back to the colony. The study emphasizes that king penguins are specialist myctophid eaters throughout their breeding range in summer, and highlights the importance of Protomyctophum choriodon as a link between zooplankton and top predators in the pelagic ecosystem of the southwestern Atlantic Ocean.     

Ornamental colors reveal age in the king penguin

We investigated whether delayed plumage maturation occurred in king penguins (Aptenodytes patagonicus). Therefore we examined the relationships between age and sex on spectral properties and size of two colored plumage patches and a UV-reflective beak spot, using known-age cohorts. Unlike the colored patch on the breast, we found age differences in ear and beak coloration. These results suggest that head ornaments in king penguins could signal sexual maturity or social status. No sex differences were found in the intensity of colored ornaments, which can result from mutual mate choice or genetic correlation between sexes. Size of colored patches did not relate to age or sex.     

Maternal telomere length inheritance in the king penguin

Telomeres are emerging as a biomarker for ageing and survival, and are likely important in shaping life-history trade-offs. In particular, telomere length with which one starts in life has been linked to lifelong survival, suggesting that early telomere dynamics are somehow related to life-history trajectories. This result highlights the importance of determining the extent to which telomere length is inherited, as a crucial factor determining early life telomere length. Given the scarcity of species for which telomere length inheritance has been studied, it is pressing to assess the generality of telomere length inheritance patterns. Further, information on how this pattern changes over the course of growth in individuals living under natural conditions should provide some insight on the extent to which environmental constraints also shape telomere dynamics. To fill this gap partly, we followed telomere inheritance in a population of king penguins (Aptenodytes patagonicus). We tested for paternal and maternal influence on chick initial telomere length (10 days old after hatching), and how these relationships changed with chick age (at 70, 200 and 300 days old). Based on a correlative approach, offspring telomere length was positively associated with maternal telomere length early in life (at 10 days old). However, this relationship was not significant at older ages. These data suggest that telomere length in birds is maternally inherited. Nonetheless, the influence of environmental conditions during growth remained an important factor shaping telomere length, as the maternal link disappeared with chicks'' age.     

Gentoo penguin Pygoscelis papua diet as an indicator of planktonic availability in the Kerguelen Islands

Since penguins rely on the main planktonic resources of the Southern Ocean, knowledge of their diet may be used for monitoring these resources During winter and spring of 1987 and 1989, we investigated the composition of the diet of gentoo penguins. Pygoscelis papua, in relation to changes in the availability of two prey species, Euphausia vallentini and Themisto gaudichaudii, sampled during plankton surveys in the Kerguelen Islands. The comparison between plankton surveys and diet analysis was performed on samples taken 2–4 km from the studied colonies. Data on the abundance of Zooplankton derived from penguins' diet matched closely those from net hauls during a year of high plankton availability (1987). On the other hand, a weaker correspondence was found during a year of restricted availability (1989). The mean sizes of amphipods caught by penguins and net hauls were very similar but the size distribution showed comparatively fewer small and large individuals in net-hauls than in penguin stomachs. Detailed studies on the feeding range and foraging effort of penguins are therefore needed in the near future to validate the potential of penguin diet as a measure of plankton abundance.     

Sexual differences in the diet of king cormorants at Macquarie Island

Sexual differences in the diet of king cormorants,Phalacrocorax albiventer, were investigated during the 1993/1994 austral summer at Macquarie Island. The major food items, identified by otoliths in regurgitations, were demersal fish; fish mass consumed could be estimated using a wet mass-otolith length relationship. Two fish species,Paranotothenia magellanica andHarpagifer georgianus, constituted 98% of the wet mass (male and female cormorants combined). Estimated individual fish mass ofParanotothenia magellanica (19.6±11.6 g) was greater than that ofH. georgianus (2.8±1.3 g). Total wet mass of food and number of fish in regurgitations did not differ statistically between the sexes of cormorants. However, males tended to feed on larger fish than did females.