Laurent Demongin

Diving seabirds share foraging space and time within and among species

Ecological theory predicts that animals with similar foraging strategies should not be able to co-exist without segregating either in space, time or diet. In communities, intra-specific competition is thought to be more intense than the competition among species, because of the lack of niche partitioning between conspecifics. Hence, while different seabird species can overlap in their foraging distribution, intra-specific competition can drive the neighboring populations of the same species to spatial segregation of foraging areas. To investigate ecological segregation within and among species of diving seabirds, we used a multi-species GPS-tracking approach of seabirds of four species on a small island in the Southwest Atlantic. The present study goes beyond previous work by analyzing simultaneous effects of species and colonies. We observed strikingly strong spatial foraging segregation among birds of the same species, breeding in colonies as close as 2 km from each other. Conspecifics from neighboring colonies used foraging places adjacent to their own colony, and there was little or no overlap with birds from the other colony. A zone with increased predator concentration was completely avoided during foraging trips, likely contributing to the spatial segregation. In addition to spatial segregation, we also observed intra-specific differences in other components of foraging behavior, such as time of day, dive depth and diet. These were most likely caused by optimal foraging of individuals in relation to habitat differences on a local scale, leading to a complex pattern of interactions with environmental covariates, in particular foraging daytime, foraging water layer temperature and depth, distance to coast and bathymetric depth of foraging areas. As mechanisms leading to the spatial segregation we propose a combination of optimal foraging and avoidance of predation.

Aspects of the breeding biology of the southern rockhopper penguin Eudyptes c. chrysocome and new consideration on the intrinsic capacity of the A-egg

The rockhopper penguins Eudyptes chrysocome have recently been split into the northern E. moseleyi and the southern E. chrysocome rockhopper penguin. It is therefore crucial to have a comprehensive understanding of the biology of each species in order to develop appropriate conservation measures. We investigated the breeding biology of the southern rockhopper on New Island, in the western part of the Falklands Islands, by following the breeding attempt of 160 pairs during the 2006/2007 season and examining the effect of lay time and colony habitat on breeding success. Specifically, we compared survival and growth parameters between A- and B-eggs and chicks from non-manipulated and artificially manipulated nests to investigate why southern rockhopper penguins in the Falkland Islands are more able to fledge an A-egg (first laid) than conspecifics elsewhere. Breeding was highly synchronous, with no significant difference in the breeding success between early and late breeders or between pairs breeding in different habitats. We demonstrate for the first time that the A-egg produced by the southern rockhopper penguin has, when alone, the same theoretical intrinsic potential to lead to a fledged chick as the B-egg. In contrast, the hatching success and survival of the B-chick was similar when alone or in a two-egg clutch.

Sexual Dimorphism and use of Morphological Measurements to Sex Adults, Immatures and Chicks of Rockhopper Penguins

Following recent phylogenetic work, Rockhopper Penguins were suggested to consist of two or three species. For the Southern Rockhopper Penguin Eudyptes c. chrysocome, sexual dimorphism has not been studied in detail, and only a few previous studies on penguins have investigated sexual dimorphism in immatures and chicks. Using data in the literature, we examined whether the sexual dimorphism of adults varies among the three taxa of Rockhopper Penguins and then we investigated the most reliable measurements to sex adult Rockhopper Penguins. We observed that bill length is the most useful measurement to separate males from females. To allow for sex discrimination in the field, we also examined a large dataset of Southern Rockhopper Penguins from New Island, Falkland Islands, including adults sexed via observation of behaviour, and immatures and chicks sexed genetically. We found that male adults and immatures were larger than females in bill length and bill depth and, to a lesser degree, in flipper lengths. We thus derived discriminant functions from bill length and bill depth and correctly sexed 96.2% of adults and 91.8% of immatures. In newly hatched chicks, males had a longer bill than females, but sexing was only successful for 63.5% of hatchlings. Just before the crèche age (18 and 19 days) and after the pre-fledging moult (55 days and older), all morphological measurements of chicks were significantly different between sexes, and sex determination was successful for 68.2% and 84.3% of chicks in these age groups, respectively. Consistently among age groups, bill length was the most dimorphic character in this population.

Maternal deposition of yolk corticosterone in clutches of southern rockhopper penguins (Eudyptes chrysocome chrysocome).

High corticosterone levels can have deleterious effects in developing avian embryos and chicks. Therefore, it may be adaptive for avian mothers to reduce corticosterone transfer to their eggs. However, until now, data about the active or/and passive role of mothers in corticosterone transfer to eggs are inconclusive. Here, we study maternal investment into A- and B-eggs of southern rockhopper penguins (Eudyptes chrysocome chrysocome). This species exhibits reversed hatching asynchrony and provides a unique model to test whether there is a strategic investment in corticosterone favoring the B-chick, which is most likely to survive. We found that rockhopper penguins had the highest yolk concentrations of any wild bird species studied so far. Contrary to our expectations, B-eggs had more yolk corticosterone both in concentration and in quantity than A-eggs, independently of the laying period and the level of human disturbance. Additionally, females deposited more yolk corticosterone in their eggs when they were disturbed. However, this disturbance effect was particularly strong for A-eggs and for late-laid eggs. The present data support neither the predictions for an active regulation nor for a passive deposition, and hormone deposition mechanisms still need to be explored. The adaptive value, if any, of high yolk corticosterone is presently unknown.

Evaluating the Impact of Handling and Logger Attachment on Foraging Parameters and Physiology in Southern Rockhopper Penguins

Logger technology has revolutionised our knowledge of the behaviour and physiology of free-living animals but handling and logger attachments may have negative effects on the behaviour of the animals and their welfare. We studied southern rockhopper penguin (Eudyptes chrysocome) females during the guard stage in three consecutive breeding seasons (2008/09−2010/11) to evaluate the effects of handling and logger attachment on foraging trip duration, dive behaviour and physiological parameters. Smaller dive loggers (TDRs) were used in 2010/11 for comparison to larger GPS data loggers used in all three seasons and we included two categories of control birds: handled controls and PIT control birds that were previously marked with passive integrative transponders (PITs), but which had not been handled during this study. Increased foraging trip duration was only observed in GPS birds during 2010/11, the breeding season in which we also found GPS birds foraging further away from the colony and travelling longer distances. Compared to previous breeding seasons, 2010/11 may have been a period with less favourable environmental conditions, which would enhance the impact of logger attachments. A comparison between GPS and TDR birds showed a significant difference in dive depth frequencies with birds carrying larger GPS data loggers diving shallower. Mean and maximum dive depths were similar between GPS and TDR birds. We measured little impact of logger attachments on physiological parameters (corticosterone, protein, triglyceride levels and leucocyte counts). Overall, handling and short-term logger attachments (1–3 days) showed limited impact on the behaviour and physiology of the birds but care must be taken with the size of data loggers on diving seabirds. Increased drag may alter their diving behaviour substantially, thus constraining them in their ability to catch prey. Results obtained in this study indicate that data recorded may also not represent their normal dive behaviour.

Geographical variation in egg size dimorphism in rockhopper penguins

All crested penguins present a unique reversed hatching asynchrony: the larger second-laid egg (B-egg) hatches before the smaller first-laid egg (A-egg). Although both eggs often hatch, the A-chick generally dies of starvation within days after hatching. However, within rockhopper penguins, the population at the Falkland Islands is unique in that some birds manage to raise both chicks. Although it has been suggested that the egg size dimorphism between A- and B-eggs may explain how long both eggs and chicks survive, this hypothesis has never been explicitly tested. We expect that both eggs are retained longer in the less dimorphic clutches than in the more dimorphic ones. In this paper, we have compiled egg measurements for three rockhopper penguin species (Eudyptes chrysocome, E. filholi and E. moseleyi) in order to compare the intra-clutch egg size dimorphism among these species. Furthermore, we have collected new data to compare egg size dimorphism between two populations of E. chrysocome (Falkland Islands versus Staten Island). A-egg volumes are more variable between species and populations than B-egg volumes. E. chrysocome and especially the population from the Falkland Islands produces the largest A-eggs and the least dimorphic eggs. Nevertheless, as differences in A-egg volumes between species and between the populations of Falkland Islands and Staten Island are stronger and more significant than differences in egg dimorphism, we suggest that A-egg volume, more than egg dimorphism, could be one of the factors influencing the prevalence of twins. A large A-egg and/or reduced egg dimorphism is probably necessary to enable rockhopper penguins to raise two chicks, but other reasons may also be involved which enable them to keep both eggs and chicks.

What ecological factors can affect albumen corticosterone levels in the clutches of seabirds? Timing of breeding, disturbance and laying order in rockhopper penguins (Eudyptes chrysocome chrysocome)

Female birds deposit corticosterone into their eggs. Elevated concentrations of this hormone may interfere with the development of their offspring, and mothers should thus regulate corticosterone levels deposited into the eggs adaptively. However, if females are unable to regulate deposition, then the corticosterone concentration in eggs should reflect that in female plasma and should be influenced by stressors to the females. We measured corticosterone levels in the albumen of rockhopper penguins, and assessed their relationship with hatching order, human disturbance and laying date. Rockhopper penguins (Eudyptes chrysocome chrysocome) lay two eggs, of which the second egg (B-egg) is larger and hatches faster than the first egg (A-egg). The chick hatching from the B-egg is also much more likely to survive than its sibling. Albumen corticosterone concentrations were lower in B-eggs. However, as B-eggs contained more albumen than A-eggs, the total corticosterone deposited in the albumen was not significantly different between the two eggs. Daily disturbance by human observers during albumen production did not influence albumen corticosterone levels. Laying date had an effect on total albumen corticosterone through a higher albumen mass. However, we observed a high individual component in the composition of eggs from the same clutch. Thus, more work is required to explore the hypotheses of passive versus active transfer to eggs and to understand the adaptive value of contrary effects on the amount and concentration of corticosterone.

Yolk androgen deposition in rockhopper penguins, a species with reversed hatching asynchrony

To maximize fitness, females should invest optimally in the siblings within a litter or brood and adapt this investment to environmental conditions. Chick mass and yolk androgens have been shown to influence the outcome of sibling competition. In birds, asynchronous hatching plays a major role in this process and often leads to brood reduction. We studied maternal deposition of yolk androgens in eggs of southern rockhopper penguins (Eudyptes chrysocome chrysocome). Contrary to other avian models, laying and hatching sequences do not coincide in this species, which exhibits reversed hatching asynchrony. This provides a unique model to test whether the first egg to hatch (B-egg), which is the most likely to survive, differs in composition from the second egg to hatch (A-egg). We found that B-eggs had higher egg masses, yolk masses, yolk androgen concentrations and total yolk androgen amounts than A-eggs. This was observed consistently for the three androgens analyzed (testosterone, androstenedione and 5α-dihydrotestosterone). Laying date affected androgen deposition into A- and B-eggs differently. Interestingly, late clutches had proportionally higher androgen levels in the B-egg compared to the A-egg than early clutches. We discuss these results in relation to the chronology of egg formation and the potential effect of the observed differences on embryo development and brood reduction.

Do leucocyte profiles reflect temporal and sexual variation in body condition over the breeding cycle in Southern Rockhopper Penguins

Southern Rockhopper Penguins (Eudyptes chrysocome chrysocome) have a strongly synchronised breeding cycle with a fixed pattern of nest attendance for males and females. We studied leucocyte profiles and the development of granulocyte/lymphocyte (G/L) ratios as an indicator of stress. Variation in G/L ratios were related to sex and breeding stage, but not individual body condition. G/L ratios were similar for males and females during the first part of the incubation period (“shared incubation”, when males and females both attend the nest), but in the second part of the incubation (“single incubation”, only one adult attends the nest), females had significantly higher G/L ratios and a lower body condition than males. The lowest G/L ratios were recorded during the crèche of the chicks at the end of the breeding season. Our results show that G/L ratios in breeding Southern Rockhopper Penguins on the population-scale reflect the temporally and sexually different timing of fasting and refeeding related to the breeding cycle. However, this measurement was not sensitive enough to reveal an effect of body condition on G/L ratios on an individual scale.ZusammenfassungSüdliche Felsenpinguine (Eudyptes chrysocome chrysocome) haben einen stark synchronisierten Brutzyklus. Während der Inkubation und Kükenaufzucht wechseln sich Männchen und Weibchen am Nest in einem festgelegten Muster ab. Wir untersuchten Leukozyten-Profile und die Entwicklung des Granulocyten/Lymphozyten (G/L) Verhältnisses als Indikator von Stress. Das G/L Verhältnis war abhängig von Geschlecht und Brutphase (Inkubation, Kükenaufzucht), aber nicht individueller Körperkondition. Männchen und Weibchen hatten ähnliche G/L Verhältnisse in der ersten Phase der Inkubation (“gemeinsame Inkubation”, wenn Männchen und Weibchen gemeinsam das Nest bewachen und die Eier bebrüten). Weibchen hatten signifikant höhere G/L Verhältnisse und geringere Körperkondition als Männchen in der zweiten Phase der Inkubation (“einzelne Inkubation”, nur ein Elternteil bleibt am Nest). Wir fanden die niedrigsten G/L Verhältnisse während der Crèche (Küken bleiben tagsüber allein und formen kleine Gruppen, sog. Crèches) am Ende des Brutzyklus. Unsere Ergebnisse zeigen, dass das G/L Verhältnis das zeitliche Muster von Fasten und Gewichtszunahme während des Brutzyklus für Männchen und Weibchen des südlichen Felsenpinguins auf Populationsebene gut widerspiegelt. Auf individueller Ebene war diese Methode jedoch nicht subtil genug um einen Effekt von Körperkondition auf das G/L Verhältnis nachzuweisen.

Yolk androgen deposition without an energetic cost for female rockhopper penguins: a compensatory strategy to accelerate brood reduction?

Whether androgen deposition in eggs is physiologically costly for female birds has remained a crucial but unsolved question, despite a broad use of this assumption in functional studies. We tested whether females depositing high androgen concentrations experienced higher mass losses than females depositing low androgen concentrations. Analysing female body mass change during egg formation in rockhopper penguins (Eudyptes chrysocome chrysocome), we observed no energetic cost to androgen deposition. Nevertheless, lighter females laid eggs with higher yolk androgen concentrations. This relationship existed only for the second-laid egg (B-egg), but not for the first-laid egg (A-egg). Since the B-egg is usually the first to hatch and the only one to produce a fledging chick, we hypothesize that differential yolk androgen deposition may be an adaptive strategy for females to affect brood reduction.