Scaling of foraging radius and growth rate in petrels and albatrosses (Procellariiformes)

first_imgData are assembled from a number of sources on several species of Procellariiformes breeding on South Georgia, covering the amount, frequency and energetic content of feeds brought to the young, and flight speeds on foraging expeditions. The rate at which energy is delivered to the young is discussed in terms of “relative delivered power”, whose dependence on foraging radius is discussed. Species in the 3-5 kg range of body mass achieve the most relative delivered power for a given foraging radius, while very large and very small species are at a disadvantage, for different reasons. When due account is taken of the scaling of time, the largest and smallest species take twice as long to fledge as those of intermediate size. The methods of scaling delivered power, growth rate and fledging time are intended to be applicable to other groups of birds read more

Acanthocephalan infection of inshore fishes at the South Orkney Islands

first_imgAn examination of notothenioid fish of three species, including 23 immature Notothenia coriiceps Richardson, revealed seven acanthocephalan species, including two Echinorhynchida occurring in the intestine and five Polymorphida in the body cavity. Four species -Metacanthocephalus johnstoni Zdzitowiecki, Corynosoma arctocephali Zdzitowiecki, C. pseudohamanni Zdzitowiecki, C.shackletoni Zdzitowiecki – are reported for the first time from the area. Polymorphida were twice as numerous as Echinorhynchida. The dominant parasites were Aspersentis megarhynchus (Linstow) and C. hamanni (Linstow) in Notothenia coriiceps, and C. bullosum (Linstow) in Chaenocephalus aceratus (Lönnberg). The infection of Notothenia coriiceps and Chaenocephalus aceratus in this area was compared with these species and Notothenia rossii Richardson in neighbouring areas. The infection of Notothenia coriiceps at the South Orkney Islands is more similar to that at the South Shetland Islands than that found at South Georgia.last_img read more

Postweaning behaviour in pups of the southern elephant seal (Mirounga leonina) on South Georgia

first_imgAfter weaning, southern elephant seal pups (Mirounga leonina) fast for 3 – 8 weeks, for largely unknown reasons. During the postweaning fast we observed daytime behaviour and movements of pups on South Georgia in relation to mass, sex, and tooth eruption. There was variation in behaviour, with the lowest levels of activity from about 09:00 to 15:00. When ashore, weaned pups spent 97% of the time resting. There was no difference in activity between the sexes, except that only male pups were observed fighting. There was a significant difference in tooth eruption between the sexes. In female pups, 87.9% had teeth at weaning, while only 28.7% of male pups had. There was no correlation between mass at weaning and activity in either sex. Weaned pups tended to gather in groups (median group size 3, range 2 – 67). Several factors may affect the behaviour of pups during the postweaning fast: the resting behaviour required to save energy favours spending time ashore during the day (which also enhances vitamin D synthesis), and foraging is more effectively practiced at night because their prey is more active at night.last_img read more

State-dependent fertility in pinnipeds: contrasting capital and income breeders

first_img1. The study tested the hypothesis that the occurrence of pregnancy in mammals that are capital breeders will be most closely related to state variables that are indices of food stores. Income breeders would not be expected to have the same relationship. 2. The study examined the relationships between mass, time of year, age and body length with the occurrence of pregnancy in three species of pinniped. This included two capital breeders (Crabeater Seal, Lobodon carcinophagus Hombron & Jacquinot, and Grey Seal, Halichoerus grypus Fabricius) and one income breeder (Antarctic Fur Seal, Arctocephalus gazella Peters). Multiple logistic regression analysis was used to examine the relationships and the interactions between the different state variables. 3. In both the capital breeders the state variables used in the study explained approximately twice the amount of variability (55% compared with 25%) in the occurrence of pregnancy than in the income breeder. Mass was the dominant state variable among both the capital breeders whereas in the income breeder mass was less important both relative to other state variables and in absolute terms. The results support the conclusion that the occurrence of pregnancy in capital breeders is more sensitive to body reserves than it is in income breeders. 4. The results also support the conclusion that life histories are the end result of a variety of functional responses to different state variables that have differing degrees of influence. In particular a size-structured approach to studies of population dynamics in pinnipeds may be a more informative way of predicting population responses to environmental variability than the more traditional age-structured approach.last_img read more

A novel joint space-wavenumber analysis of an unusual Antarctic gravity wave event

first_imgAs part of a collaborative research program between British Antarctic Survey, U.K. and Utah State University, USA, all sky airglow images were recorded at Halley Station Antarctica (75.5 S, 26.7 W). An unusual mesospheric gravity wave event was observed in the OH nightglow (nominal height ≈87 km) over a period of ≈3 hours on the 27–28 May, 2001. The characteristics of the bore wave event were determined by application of the one dimensional spatial S-Transform analysis. This is the first time such analysis has been performed on airglow data. By employing these local spatial spectral analysis, the evolution of the wave packet can be measured. The wave parameters (phase velocity, wave number, wavelength, period) were inferred from as little as 2 images (separated in time), which is a powerful ability when a data set of images is irregularly sampled in time, as is often the case in airglow imager studies. Several interesting and novel results were obtained regarding the dynamic evolution of the wave. The horizontal wavelength of the bore wave packet was seen to decrease as the packet evolved. Coincident with this observation, the horizontal phase speed decreased, with an associated decrease in wave packet amplitude.last_img read more

The relationship between the Southern Hemisphere Annular Mode and Antarctic Peninsula summer temperatures: analysis of a high-resolution model climatology

first_imgThe large regional summer warming on the east coast of the northern Antarctic Peninsula (AP), which has taken place since the mid-1960s, has previously been proposed to be caused by a trend in the Southern Hemisphere Annular Mode (SAM). The authors utilize a high-resolution regional atmospheric model climatology (14-km grid spacing) to study the mechanisms that determine the response of the near-surface temperature to an increase in the SAM (Delta T/Delta SAM). Month-to-month variations in near-surface temperature and surface pressure are well represented by the model. It is found that north of similar to 68 degrees S, Delta T/Delta SAM is much larger on the eastern (lee) side than on the western (windward) side of the barrier. This is because of the enhanced westerly flow of relatively warm air over the barrier, which warms (and dries) further as it descends down the lee slope. The downward motion on the eastern side of the barrier causes a decrease in surface-mass balance and cloud cover. South of similar to 68 degrees S, vertical deflection across the barrier is greatly reduced and the contrast in Delta T/Delta SAM between the east and west sides of the barrier vanishes. In the northeastern part of the AP, the modeled Delta T/Delta SAM distribution is similar to the distribution derived from satellite infrared radiometer data. The region of strongest modeled temperature sensitivity to the SAM is where ice shelf collapse has recently taken place and does not extend farther south over the Larsen-C Ice Shelf.last_img read more

Nonlinear trends, long-range dependence and climate noise properties of surface temperature

first_imgThis study investigates the significance of trends of four temperature time series—Central England Temperature(CET), Stockholm, Faraday-Vernadsky, and Alert. First the robustness and accuracy of various trend detectionmethods are examined: ordinary least squares, robust and generalized linear model regression, Ensemble EmpiricalMode Decomposition (EEMD), and wavelets. It is found in tests with surrogate data that these trenddetection methods are robust for nonlinear trends, superposed autocorrelated fluctuations, and non-Gaussianfluctuations. An analysis of the four temperature time series reveals evidence of long-range dependence (LRD)and nonlinear warming trends. The significance of these trends is tested against climate noise. Three differentmethods are used to generate climate noise: (i) a short-range-dependent autoregressive process of first order[AR(1)], (ii) an LRD model, and (iii) phase scrambling. It is found that the ability to distinguish the observedwarming trend from stochastic trends depends on the model representing the background climate variability.Strong evidence is found of a significant warming trend at Faraday-Vernadsky that cannot be explained by any ofthe three null models. The authors find moderate evidence of warming trends for the Stockholm and CET timeseries that are significant against AR(1) and phase scrambling but not the LRD model. This suggests that thedegree of significance of climate trends depends on the null model used to represent intrinsic climate variability.This study highlights that in statistical trend tests, more than just one simple null model of intrinsic climate variabilityshould be used. This allows one to better gauge the degree of confidence to have in the significance of trends.last_img read more

Recent trends in numbers of wandering (Diomedea exulans), black-browed (Thalassarche melanophris) and grey-headed (T. chrysostoma) albatrosses breeding at South Georgia

first_imgSouth Georgia supports globally important populations of seabirds, including the wandering albatross Diomedea exulans, black-browed albatross Thalassarche melanophris and grey-headed albatross T. chrysostoma, currently classified by the world Conservation Union (IUCN) as vulnerable, near threatened and endangered, respectively. Surveys of these species at South Georgia were conducted during the incubation stage in November 2014 to January 2015, repeating previous surveys conducted in the 2003/2004 season. Numbers of wandering albatrosses breeding annually at South Georgia decreased by 18% (1.8% per year) from 1553 pairs in 2003/2004 to an estimated 1278 pairs in 2014/2015. Over the same period, black-browed and grey-headed albatrosses decreased by 19% (1.9% per year) and 43% (5% per year), respectively. These represent a continuation of negative trends at South Georgia since the 1970s and are in contrast to some populations elsewhere, which have shown signs of recent recovery. Given the importance of South Georgia for these species, the ongoing population declines, and in the case of grey-headed albatrosses, an acceleration of the decline is of major conservation concern. Incidental fisheries mortality (bycatch) is currently considered to be the main threat. Although seabird bycatch has been reduced to negligible levels in the fisheries operating around South Georgia, wider implementation of effective seabird bycatch mitigation measures is required to improve the conservation status of the South Georgia populations of wandering, black-browed and grey-headed albatrosses. In addition, more research is required to investigate the respective roles of bycatch and climate change in driving these population trends.last_img read more

Subglacial lakes and hydrology across the Ellsworth Subglacial Highlands, West Antarctica

first_imgSubglacial water plays an important role in ice sheet dynamics and stability. Subglacial lakes are often located at the onset of ice streams and have been hypothesised to enhance ice flow downstream by lubricating the ice–bed interface. The most recent subglacial-lake inventory of Antarctica mapped nearly 400 lakes, of which ∼ 14 % are found in West Antarctica. Despite the potential importance of subglacial water for ice dynamics, there is a lack of detailed subglacial-water characterisation in West Antarctica. Using radio-echo sounding data, we analyse the ice–bed interface to detect subglacial lakes. We report 33 previously uncharted subglacial lakes and present a systematic analysis of their physical properties. This represents a ∼ 40 % increase in subglacial lakes in West Antarctica. Additionally, a new digital elevation model of basal topography of the Ellsworth Subglacial Highlands was built and used to create a hydropotential model to simulate the subglacial hydrological network. This allows us to characterise basal hydrology, determine subglacial water catchments and assess their connectivity. We show that the simulated subglacial hydrological catchments of the Rutford Ice Stream, Pine Island Glacier and Thwaites Glacier do not correspond to their ice surface catchments.last_img read more