Nina Dehnhard

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.

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.

Variability of higher trophic level stable isotope data in space and time – a case study in a marine ecosystem

RATIONALE 1In shelf and coastal ecosystems, planktonic and benthic trophic pathways differ in their carbon stable isotope ratios (δ(13)C values) and nitrogen stable isotope ratios (δ(15)N values) and they increase predictably with trophic level. Stable isotope data are therefore used as a tool to study food webs in shelf and coastal ecosystems, and to assess the diets and foraging behaviour of predators. However, spatial differences and temporal changes in prevailing environmental conditions and prey abundance may lead to considerable heterogeneity in stable isotope values measured in focal animal species. METHODS Here we assess spatial and temporal variability of δ(13)C and δ(15)N values in tissue samples of fish, squid and crustacean species captured over three years during research cruises close to the Falkland Islands, Southwest Atlantic. RESULTS Both in δ(15)N values and especially in δ(13)C values, intra-species differences were large and often exceeded inter-species differences. Spatial patterns were weak, albeit statistically significant. The distribution of δ(13)C values was related to latitude, while the δ(15)N values varied with longitude. The distance from the coast and depth of catch influenced both δ(13)C and δ(15)N values. However, the importance of temporal variability greatly exceeded that of spatial variability. In addition to a moderate overall seasonal effect, we found that species differed strongly in their specific seasonal changes. CONCLUSIONS Seasonal differences in the relative position of species or species groups in the C-N isotope space suggest changes in the utilisation of planktonic vs. benthic trophic pathways, indicating flexible foraging strategies in response to variable environmental conditions. These seasonal differences should be taken into account when analysing higher trophic level feeding ecology with stable isotope analysis.

Females Paired with New and Heavy Mates Reduce Intra- Clutch Differences in Resource Allocation

Reproductive investment affects both offspring and parental fitness and influences the evolution of life histories. Females may vary their overall primary reproductive effort in relation to the phenotypic characteristics of their mate. However, the effects of male quality on differential resource allocation within clutches have been largely neglected despite the potential implications for mate choice and population dynamics, especially in species exhibiting biparental care and brood reduction. Female southern rockhopper penguins Eudyptes chrysocome paired with heavy mates reduced intra-clutch variation in egg and albumen masses. Females paired with new mates also reduced intra-clutch variation in yolk androgen levels. Since both an increased mass and increased androgen concentrations positively influence chick survival under sibling competition, the chances of fledging the whole clutch are likely to be higher for newly formed pairs with heavy males than for previously formed pairs with light males. Interestingly, total clutch provisioning did not vary with male quality. We show for the first time that females vary intra-clutch variation in resource allocation according to male quality. In species with brood reduction, it may be more adaptive for females to modulate the distribution of resources within the clutch according to breeding conditions, than to change their total clutch provisioning.

Individual consistency and phenotypic plasticity in rockhopper penguins: female but not male body mass links environmental conditions to reproductive investment.

In marine habitats, increasing ocean temperatures due to global climate change may distinctly reduce nutrient and consequently food availability for seabirds. Food availability is a known driver of body mass and reproductive investment in birds, but these traits may also depend on individual effects. Penguins show extreme intra-annual body mass variation and rely on accumulated body reserves for successful breeding. However, no study so far has tested individual consistency and phenotypic responses in body mass and reproductive investment in this taxon. Using a unique dataset on individually marked female and male southern rockhopper penguins (Eudyptes chrysocome chrysocome) across six years, we investigated 1) the individual consistency in body mass (measured at egg laying), body condition and reproductive investment across years, subsequently 2) identified the best-explanatory temperature-related environmental variables for female and male body mass, and 3) tested the effect of female and male body mass on reproductive investment. Body mass, body condition and reproductive investment were all highly repeatable. As body condition should control for the structural size of the birds, the similarly high repeatability estimates for body mass and body condition suggested that the consistent between-individual body mass differences were independent of structural size. This supported the use of body mass for the subsequent analyses. Body mass was higher under colder environmental conditions (positive Southern Annular Mode), but the overall phenotypic response appeared limited. Reproductive investment increased with female but not male body mass. While environmental effects on body mass in our study period were rather small, one can expect that ongoing global climate change will lead to a deterioration of food availability and we might therefore in the long-term expect a phenotypical decline in body mass and reproductive investment.

Plasticity in foraging behaviour and diet buffers effects of inter- annual environmental differences on chick growth and survival in southern rockhopper penguins Eudyptes chrysocome chrysocome

In marine ecosystems, primary productivity and consequently food availability for higher trophic levels are often strongly affected by the water temperature. Thus, differences in sea surface temperatures (SST) may lead to differences in the diet composition of predators, but this link is still unknown in many species. By combining GPS tracking and dive analyses on chick-rearing southern rockhopper penguins (Eudyptes chrysocome chrysocome) with stable isotope analyses and monitoring of chick growth rates and chick survival, we here attempted a comprehensive assessment of the effects of inter-annual environmental variability as indicated by SST and chlorophyll a (reflecting primary productivity) data. Inter-annual differences in environmental variables around our study colony on New Island, Falkland/Malvinas Islands, contradicted the general expectation, with higher chlorophyll a concentrations coinciding with higher spring SST in 2010/2011 compared to 2009/2010. Penguins foraged further away from the colony during guard and crèche in 2010/2011 compared to 2009/2010, while performing deeper dives in 2009/2010. Stable isotope mixing models suggested a crustacean-dominated chick diet in 2009/2010, compared to a mixture of squid and fish in 2010/2011. These differences in foraging behaviour and diet, however, had no consequences for chick growth rates or chick survival and thus had no apparent effect on population trajectories. Potentially, environmental conditions in both years could still be seen as favourable compared to other years and breeding sites, enabling the parental birds to buffer the environmental differences by plastic foraging behaviour.

Two eggs, two different constraints: a potential explanation for the puzzling intraclutch egg size dimorphism in Eudyptes penguins.

Phenotypic plasticity and phenotypic stability are major components of the adaptive evolution of organisms to environmental variation. The invariant two-egg clutch size of Eudyptes penguins has recently been proposed to be a unique example of a maladaptive phenotypic stability, while their egg mass is a plastic trait. We tested whether this phenotypic plasticity during reproduction might result from constraints imposed by migration (migratory carry-over effect) and breeding (due to the depletion of female body reserves). For the first time, we examined whether these constraints differ between eggs within clutches and between egg components (yolk and albumen). The interval between colony return and clutch initiation positively influenced the yolk mass, the albumen mass, and the subsequent total egg mass of first-laid eggs. This time interval had only a slight negative influence on the yolk mass of second-laid eggs and no influence on their albumen and subsequent total masses. For both eggs, female body mass at laying positively influenced albumen and total egg masses. Female investment into the entire clutch was not related to the time in the colony before laying but increased with female body mass. These novel results suggest that the unique intraclutch egg size dimorphism exhibited in Eudyptes penguins, with first-laid eggs being consistently smaller than second-laid eggs, might be due to a combination of constraints: a migratory carry-over effect on the first-laid egg and a body reserve depletion effect on the second-laid egg. Both these constraints might explain why the timing of reproduction, especially egg formation, is narrow in migratory capital breeders.