Survival in king penguins Aptenodytes patagonicus : temporal and sex-specific effects of environmental variability (original) (raw)
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2019
1Individuals differ in many ways. Most produce few offspring; a handful produce many. Some die early; others live to old age. It is tempting to attribute these differences in out-comes to differences in individual traits, and thus in the demographic rates experienced. However, there is more to individual variation than meets the eye of the biologist. Even among individuals sharing identical traits, life history outcomes will vary due to individual stochasticity, i.e., to chance. Quantifying the contributions of heterogeneity and chance is essential to understanding natural variability. Inter-individual differences vary across environmental conditions. Heterogeneity and stochasticity depend on environmental conditions. We show that favorable conditions increase the contributions of individual stochasticity, and reduce the contributions of heterogeneity, to variance in demographic outcomes in a seabird population. The opposite is true under poor conditions. This result has important c...
Nonlinear effects of winter sea ice on the survival probabilities of Adélie penguins
Oecologia, 2009
The population dynamics of Antarctic seabirds are influenced by variations in winter sea ice extent and persistence; however, the type of relationship differs according to the region and the demographic parameter considered. We used annual presence/absence data obtained from 1,138 individually marked birds to study the influence of environmental and individual characteristics on the survival of Adélie penguins Pygoscelis adeliae at Edmonson Point (Ross Sea, Antarctica) between 1994 and 2005. About 25% of 600 birds marked as chicks were reobserved at the natal colony. The capture and survival rates of Adélie penguins at this colony increased with the age of individuals, and five age classes were identified for both parameters. Mean adult survival was 0.85 (SE = 0.01), and no effect of sex on survival was evident. Breeding propensity, as measured by adult capture rates, was close to one, indicating a constant breeding effort through time. Temporal variations in survival were best explained by a quadratic relationship with winter sea ice extent anomalies in the Ross Sea, suggesting that for this region optimal conditions are intermediate between too much and too little winter sea ice. This is likely the result of a balance between suitable wintering habitat and food availability. Survival rates were not correlated with the Southern Oscillation Index. Low adult survival after a season characterized by severe environmental conditions at breeding but favorable conditions during winter suggested an additional mortality mediated by the reproductive effort. Adélie penguins are sensitive indicators of environmental changes in the Antarctic, and the results from this study provide insights into regional responses of this species to variability in winter sea ice habitat.
Journal of Animal Ecology, 2014
1. Understanding the demographic response of free-living animal populations to different drivers is the first step towards reliable prediction of population trends. 2. Penguins have exhibited dramatic declines in population size, and many studies have linked this to bottom-up processes altering the abundance of prey species. The effects of individual traits have been considered to a lesser extent, and top-down regulation through preda-tion has been largely overlooked due to the difficulties in empirically measuring this at sea where it usually occurs. 3. For 10 years (2003-2012), macaroni penguins (Eudyptes chrysolophus) were marked with subcutaneous electronic transponder tags and re-encountered using an automated gateway system fitted at the entrance to the colony. We used multistate mark-recapture modelling to identify the different drivers influencing survival rates and a sensitivity analysis to assess their relative importance across different life stages. 4. Survival rates were low and variable during the fledging year (mean = 0Á33), increasing to much higher levels from age 1 onwards (mean = 0Á89). We show that survival of macaroni penguins is driven by a combination of individual quality, top-down predation pressure and bottom-up environmental forces. The relative importance of these covariates was age specific. During the fledging year, survival rates were most sensitive to top-down predation pressure, followed by individual fledging mass, and finally bottom-up environmental effects. In contrast , birds older than 1 year showed a similar response to bottom-up environmental effects and top-down predation pressure. 5. We infer from our results that macaroni penguins will most likely be negatively impacted by an increase in the local population size of giant petrels. Furthermore, this population is, at least in the short term, likely to be positively influenced by local warming. More broadly, our results highlight the importance of considering multiple causal effects across different life stages when examining the survival rates of seabirds.
Global Change Biology, 2008
The consequences of warming for Antarctic long-lived organisms depend on their ability to survive changing patterns of climate and environmental variation. Among birds and mammals of different Antarctic regions, including emperor penguins, snow petrels, southern fulmars, Antarctic fur seals and Weddell seals, we found strong support for selection of life history traits that reduce interannual variation in fitness. These species maximize fitness by keeping a low interannual variance in the survival of adults and in their propensity to breed annually, which are the vital rates that influence most the variability in population growth rate (λ). All these species have been able to buffer these rates against the effects of recent climate-driven habitat changes except for Antarctic fur seals, in the Southwest Atlantic. In this region of the Southern Ocean, the rapid increase in ecosystem fluctuation, associated with increasing climate variability observed since 1990, has limited and rendered less predictable the main fur seal food supply, Antarctic krill. This has increased the fitness costs of breeding for females, causing significant short-term changes in population structure through mortality and low breeding output. Changes occur now with a frequency higher than the mean female fur seal generation time, and therefore are likely to limit their adaptive response. Fur seals are more likely to rely on phenotypic plasticity to cope with short-term changes in order to maximize individual fitness. With more frequent extreme climatic events driving more frequent ecosystem fluctuation, the repercussions for life histories in many Antarctic birds and mammals are likely to increase, particularly at regional scales. In species with less flexible life histories that are more constrained by fluctuation in their critical habitats, like sea-ice, this may cause demographic changes, population compensation and changes in distribution, as already observed in penguin species living in the Antarctic Peninsula and adjacent islands.
Ecological Applications, 2019
We developed a Hidden Markov mark–recapture model (R package marked) to examine sex‐specific demography in Magellanic Penguins (Spheniscus magellanicus). Our model was based on 33 yr of resightings at Punta Tombo, Argentina, where we banded ~44,000 chicks from 1983 to 2010. Because we sexed only 57% of individuals over their lifetime, we treated sex as an uncertain state in our model. Our goals were to provide insight into the population dynamics of this declining colony, to inform conservation of this species, and to highlight the importance of considering sex‐specific vital rates in demographic seabird studies. Like many other seabirds, Magellanic Penguins are long‐lived, serially monogamous, and exhibit obligate biparental care. We found that the non‐breeding‐season survival of females was lower than that of males and that the magnitude of this bias was highest for juveniles. Biases in survival accumulated as cohorts aged, leading to increasingly skewed sex ratios. The survival bias was greatest in years when overall survival was low, that is, females fared disproportionality worse when conditions were unfavorable. Our model‐estimated survival patterns are consistent with independent data on carcasses from the species’ non‐breeding grounds, showing that mortality is higher for juveniles than for adults and higher for females than for males. Juveniles may be less efficient foragers than adults are and, because of their smaller size, females may show less resilience to food scarcity than males. We used perturbation analysis of a population matrix model to determine the impact of sex‐biased survival on adult sex ratio and population growth rate at Punta Tombo. We found that adult sex ratio and population growth rate have the greatest proportional response, that is, elasticity, to female pre‐breeder and adult survival. Sex bias in juvenile survival (i.e., lower survival of females) made the greatest contribution to population declines from 1990 to 2009. Because starvation is a leading cause of morality in juveniles and adults, precautionary fisheries and spatial management in the region could help to slow population decline. Our data add to growing evidence that knowledge of sex‐specific demography and sex ratios are necessary for accurate assessment of seabird population trends.
Journal of Zoology, 2006
Life-history theory predicts that adults of long-lived species such as seabirds should optimally balance investment in current and future offspring. However, when trying to optimize investment in offspring provisioning, the most energetically costly component of seabird parental care, adults need to contend with large interannual fluctuations in prey availability and hence the cost of chick provisioning. Adults faced with this uncertainty can mechanistically balance parental care by adopting a strategy somewhere along the continuum between maintaining constant investment in foraging effort between years and letting chick provisioning fluctuate or holding chick provisioning constant and varying investment in foraging effort. Using ship-based hydroacoustic assessment of prey, time-depth recorders attached to penguins and land-based observations at the breeding colony, we examined how foraging and reproductive effort in breeding chinstrap penguins Pygoscelis antarctica responded to interannual variation in the abundance of Antarctic krill Euphausia superba in the vicinity of Seal Island, South Shetland Islands, 1990-1992. Regional measures of krill density varied by a factor of 2. 5 (47.0, 23.8 and 61.2 g m À2 in 1990, 1991 and 1992, respectively) and was correlated with annual measures of breeding adult body weight and reproductive performance (breeding population size, duration of chick rearing, chick growth, breeding success and fledgling weight). In contrast, measures of penguin foraging effort (dive depth, dive duration, number of trips day À1 , trip duration, number of dives trip À1 and dive rate) did not differ between years. We conclude that chinstrap penguins reduce reproductive success rather than increase foraging effort in response to decreases in prey abundance in a manner consistent with predictions of life-history strategies for long-lived seabirds.
Journal of Zoology, 2006
Life-history theory predicts that adults of long-lived species such as seabirds should optimally balance investment in current and future offspring. However, when trying to optimize investment in offspring provisioning, the most energetically costly component of seabird parental care, adults need to contend with large interannual fluctuations in prey availability and hence the cost of chick provisioning. Adults faced with this uncertainty can mechanistically balance parental care by adopting a strategy somewhere along the continuum between maintaining constant investment in foraging effort between years and letting chick provisioning fluctuate or holding chick provisioning constant and varying investment in foraging effort. Using ship-based hydroacoustic assessment of prey, time-depth recorders attached to penguins and land-based observations at the breeding colony, we examined how foraging and reproductive effort in breeding chinstrap penguins Pygoscelis antarctica responded to interannual variation in the abundance of Antarctic krill Euphausia superba in the vicinity of Seal Island, South Shetland Islands, 1990-1992. Regional measures of krill density varied by a factor of 2.5 (47.0, 23.8 and 61.2 g m À2 in 1990, 1991 and 1992, respectively) and was correlated with annual measures of breeding adult body weight and reproductive performance (breeding population size, duration of chick rearing, chick growth, breeding success and fledgling weight). In contrast, measures of penguin foraging effort (dive depth, dive duration, number of trips day À1 , trip duration, number of dives trip À1 and dive rate) did not differ between years. We conclude that chinstrap penguins reduce reproductive success rather than increase foraging effort in response to decreases in prey abundance in a manner consistent with predictions of life-history strategies for long-lived seabirds.
Marine Ecology Progress Series, 2012
Ocean temperature has been shown to be related to various demographic parameters in several seabird species, but ultimately its influence on breeding success and survival are paramount. The timing and success of breeding of little penguins Eudyptula minor in south-eastern Australia have been shown to correlate with local sea-surface temperatures (SST) and the east−west sea-temperature gradient across Bass Strait several months earlier. However, the causal links between ocean temperature and these demographic variables are not readily apparent due to their lagged nature. Using 41 yr of data on little penguins in south-eastern Australia, we carried out a mark-recapture analysis to examine if the changing SST and sea-temperature gradient (east−west difference between 2 locations in Bass Strait) are associated with survival probability in the first year of life. First-year survival is correlated with (1) an east−west sea-temperature gradient in Bass Strait in the winter after fledging, with an increased temperature gradient associated with decreased survival and (2) the mean SST in the autumn after fledging, with warmer seas associated with increased survival. SST alone does not provide the best model for explaining first-year survival. Projections suggest that SST in south-eastern Australia and sea-temperature gradient in Bass Strait will both increase due to global warming. The net effect of an increased sea-temperature gradient in winter (which has a negative influence) and increased SST in autumn (which has a positive influence) on first-year survival is uncertain, given the current lack of knowledge concerning the relationship between the sea-temperature gradient and SST in Bass Strait.
Marine Ecology Progress Series, 2002
Pelagic seabirds depend on resources far out at sea and for which the availability can vary greatly. King penguins rely essentially on myctophid fish, which in summer are mostly available 400 to 500 km south of the Crozet Archipelago at the Antarctic Polar Front. Incubating male King penguins anticipate a possible delay in the return of the female by storing food in their stomach for several weeks, which enables them to feed the chick quickly if hatching occurs. We investigated the foraging trip duration, adult body mass regulation and the meal size for chicks relative to the laying date and the Polar Front position. We compared, in both early and late breeders, the energy content and the chemical and diet composition of the meals stored in their stomachs. During food storage by the male, the cessation of digestive processes was not complete as the meal showed some modifications of the biochemical composition, especially a decrease in lipid content; this is in contrast to oil storage in albatrosses and petrels, in which there is an increase in lipid content. On average, females came back from their second foraging trip at sea a short time before hatching. However, the trip durations were particularly variable depending on date and year, and as a consequence hatching occurred with either the female or the male incubating the egg. Late breeders showed longer foraging trip duration and built up larger fuel reserves than early breeders. Their energetic output per day foraging at sea was much lower than for early breeders. These differences in foraging trip durations of males were linked to a change in marine resource availability because, in spite of being at the same stage of the breeding cycle, male late breeders caught different prey compared to male early breeders. We assume that this strategy of long-term food storage and conservation in the stomach while fasting evolved in response to the unpredictable variations of water mass positions.