Tracey Rogers | The University of New South Wales (original) (raw)

Foraging & Spatial ecology by Tracey Rogers

For effective species management, understanding population structure and distribution is critical... more For effective species management, understanding population structure and distribution is critical. However, quantifying population structure is not always straightforward. Within the Southern Hemisphere, the blue whale (Balaenoptera musculus) complex is extremely diverse but difficult to study. Using automated detector methods, we identified “acoustic populations” of whales producing region-specific call types. We examined blue whale call types in passive acoustic data at sites spanning over 7,370 km across the southeast Indian Ocean and southwest Pacific Ocean (SWPO) from 2009 to 2012. In the absence of genetic resolution, these acoustic populations offer unique information about the blue whale population complex. We found that the Australian continent acts as a geographic boundary, separating Australia and New Zealand blue whale acoustic populations at the junction of the Indian and Pacific Ocean basins. We located blue whales in previously undocumented locations, including the far SWPO, in the Tasman Sea off the east coast of Australia, and along the Lau Basin near Tonga. Our understanding of population dynamics across this broad scale has significant implications to recovery and conservation management for this endangered species, at a regional and global scale.

Polar Biology, 2003

Data on the timing of pupping by the three species of phocid that breed on the Antarctic pack-ice... more Data on the timing of pupping by the three species of phocid that breed on the Antarctic pack-ice (crabeater, Ross and leopard seals) are limited. Better information would improve our understanding of these species' population and reproductive ecologies, and could facilitate planning and design of population surveys. Observations of the presence or absence of pups with adults during numerous voyages of the Australian National Antarctic Research Expeditions to East Antarctica during spring and early summer months are analysed and presented. The earliest sighting in any year of a crabeater pup accompanied by an adult was on 2 October and the latest sighting on 15 December. The ratio of crabeater pups to adults increased rapidly during the 10-day period 16–25 October, implying a pulse of births over this time. Ross seal pups with an accompanying adult were sighted between 24 October and 22 November, with a peak in the pup-adult ratio occurring in the period 6–15 November. Leopard seal pups were sighted between 8 November and 25 December, with the pup-adult ratio relatively constant during this period. The data provide circumstantial evidence that the maximum durations of lactation reported in the literature for the three species may be over-estimates. If lactation is shorter than reported, asynchrony in the timing of pupping, either among or within years, is implied.

Biological Conservation, 2012

The compound effects of changing habitats, ecosystem interactions, and fishing practices have imp... more The compound effects of changing habitats, ecosystem interactions, and fishing practices have implications for the management of Antarctic krill and conservation of its predators. For Antarctic pack-ice seals, an important group of krill predators, we estimate the density and krill consumption in the West Antarctic Peninsula (WAP)-Western Weddell Sea area, the main fishery region; and we consider long-term changes in suitable pack-ice habitat, increased fishing pressure and potential krill declines based upon predictions from declines in sea ice cover. More than 3 million crabeater seals consumed over 12 million tonnes of krill each year. This was approximately 17% of the krill standing stock. The highest densities of pack ice seals where found in the WAP, including in its small-scale fishery management areas, where apparently suitable seal habitat has declined by 21-28% over a 30 year period, where krill density is likely to have declined, and fishing has increased. The highest seal density was found in the Marguerite Bay area which is a source of krill for the Antarctic Peninsula and elsewhere. Significant sea-ice loss since 1979 has already occurred, leading to open water and possible expansion for the fishery in the future. These factors may combine to potentially reduce food for pack ice seals. Therefore, high uncertainty in krill and seal stock trends and in their environmental drivers call for a precautionary management of the krill fishery, in the absence of survey data to support management based on specific conservation objectives for pack-ice seals.

The method traditionally used to estimate pack-ice seal abundance employs sighting surveys from s... more The method traditionally used to estimate pack-ice seal abundance employs sighting surveys from ships or aircraft to estimate the number of seals hauled out on the ice, combined with studies of haul-out behaviour to estimate the proportion of time spent on the ice. Application of this approach has been improved in recent times by developments in survey methodology and satellite technology that theoretically allow biases in the estimation of hauled-out abundance and haulout behaviour to be accounted for that previously could not be addressed. A survey using these conventional but state-ofthe-art methods was undertaken in the summer of 1999/2000 off east Antarctica between longitudes 641E and 1501E to estimate the abundance of leopard (Hydrurga leptonyx) and other pack-ice seal species. Because they are either uncommon or very cryptic, very few leopard seals were encountered despite a large survey effort. This presented challenges in both application of the methods and analysis of the data. Abundance estimates were derived using a number of plausible predictive models. The model considered as the most reliable returned best estimates of 7300 and 12,100 for definite and definite plus probable leopard seal sightings, respectively, with 95% confidence intervals of 3700-14,500 and 7100-23,400. These estimates are likely to be negatively biased and should be treated as minimum estimates only. r

Mixing models are used to determine diets where the number of prey items are greater than one, ho... more Mixing models are used to determine diets where the number of prey items are greater than one, however, the limitation of the linear mixing method is the lack of a unique solution when the number of potential sources is greater than the number (n) of isotopic signatures +1. Using the IsoSource program all possible combinations of each source contribution (0-100%) in preselected small increments can be examined and a range of values produced for each sample analysed. We propose the use of a Moore Penrose (M-P) pseudoinverse, which involves the inverse of a 2x2 matrix. This is easily generalized to the case of a single isotope with (p) prey sources and produces a specific solution. The Antarctic leopard seal (Hydrurga leptonyx) was used as a model species to test this method. This seal is an opportunistic predator, which preys on a wide range of species including seals, penguins, fish and krill. The M-P method was used to determine the contribution to diet from each of the four prey types based on blood and fur samples collected over three consecutive austral summers. The advantage of the M-P method was the production of a vector of fractions f for each predator isotopic value, allowing us to identify the relative variation in dietary proportions. Comparison of the calculated fractions from this method with 'means' from IsoSource allowed confidence in the new approach for the case of a single isotope, N.

Marine Ecology-progress Series, 2005

In order to assess seasonal and spatial changes in diet, the δ15N and δ13C signatures of vibrissa... more In order to assess seasonal and spatial changes in diet, the δ15N and δ13C signatures of vibrissae from leopard seals Hydrurga leptonyx obtained from Prydz Bay, Eastern Antarctica, were compared with those of a captive seal on a known diet. Using the isotopic signatures of known prey, and those revealed by the assimilation rates of vibrissae, we constructed trophic models to estimate diet composition. Assuming that current diet was reflected only in the actively growing portion of the vibrissae, the latter were sectioned. Each section was then analysed independently. Two methods of analysis of the vibrissae isotopic data were compared in order to ascertain the best analytical approach to these data. A simple linear model and a von Bertalanffy growth model were used to estimate section age and vibrissae growth rates. The age predictions of the von Bertalanffy growth model allowed the existence of repeated seasonal oscillations in both δ15N and δ13C values. Temporal variations in stable isotope ratios consistent with changes in source of feeding (inshore vs. offshore) and prey types were identified in the Antarctic leopard seals, but not in the captive seal. This preliminary study has possible implications for the use of vibrissae to track dietary changes over time and may serve as a tool for investigating foraging preferences of highly mobile or migratory pinniped species.

Proceedings. Biological sciences / The Royal Society, Jan 22, 2014

Predator-prey relationships and trophic levels are indicators of community structure, and are imp... more Predator-prey relationships and trophic levels are indicators of community structure, and are important for monitoring ecosystem changes. Mammals colonized the marine environment on seven separate occasions, which resulted in differences in species' physiology, morphology and behaviour. It is likely that these changes have had a major effect upon predator-prey relationships and trophic position; however, the effect of environment is yet to be clarified. We compiled a dataset, based on the literature, to explore the relationship between body mass, trophic level and predator-prey ratio across terrestrial (n = 51) and marine (n = 56) mammals. We did not find the expected positive relationship between trophic level and body mass, but we did find that marine carnivores sit 1.3 trophic levels higher than terrestrial carnivores. Also, marine mammals are largely carnivorous and have significantly larger predator-prey ratios compared with their terrestrial counterparts. We propose that p...

PLoS ONE, 2014

Predator-prey body mass relationships are a vital part of food webs across ecosystems and provide... more Predator-prey body mass relationships are a vital part of food webs across ecosystems and provide key information for predicting the susceptibility of carnivore populations to extinction. Despite this, there has been limited research on the minimum and maximum prey size of mammalian carnivores. Without information on large-scale patterns of prey mass, we limit our understanding of predation pressure, trophic cascades and susceptibility of carnivores to decreasing prey populations. The majority of studies that examine predator-prey body mass relationships focus on either a single or a subset of mammalian species, which limits the strength of our models as well as their broader application. We examine the relationship between predator body mass and the minimum, maximum and range of their prey's body mass across 108 mammalian carnivores, from weasels to baleen whales (Carnivora and Cetacea). We test whether mammals show a positive relationship between prey and predator body mass, as in reptiles and birds, as well as examine how environment (aquatic and terrestrial) and phylogenetic relatedness play a role in this relationship. We found that phylogenetic relatedness is a strong driver of predator-prey mass patterns in carnivorous mammals and accounts for a higher proportion of variance compared with the biological drivers of body mass and environment. We show a positive predator-prey body mass pattern for terrestrial mammals as found in reptiles and birds, but no relationship for aquatic mammals. Our results will benefit our understanding of trophic interactions, the susceptibility of carnivores to population declines and the role of carnivores within ecosystems.

The behaviour of leopard seals, Hydrurga leptonyx, feeding on Adélie penguins, Pygoscelis adeliae... more The behaviour of leopard seals, Hydrurga leptonyx, feeding on Adélie penguins, Pygoscelis adeliae, was investigated between November 1993 and January 1994 in Prydz Bay, Antarctica. The seals were distributed along the fast-ice edge in locations where departing penguins congregated. Five different hunting techniques were observed, four of which were used through most of the summer. Individual leopard seals favoured specific hunting techniques. Hitherto, penguin hunting was believed to be carried out primarily by a few male seals; in this study, however, the predation observed involved many different individuals of both sexes. It is estimated that six leopard seals feeding in this area over a period of 120 days would consume 2.7% of the adult penguin population.

Data on the timing of pupping by the three species of phocid that breed on the Antarctic pack-ice... more Data on the timing of pupping by the three species of phocid that breed on the Antarctic pack-ice (crabeater, Ross and leopard seals) are limited. Better information would improve our understanding of these species' population and reproductive ecologies, and could facilitate planning and design of population surveys. Observations of the presence or absence of pups with adults during numerous voyages of the Australian National Antarctic Research Expeditions to East Antarctica during spring and early summer months are analysed and presented. The earliest sighting in any year of a crabeater pup accompanied by an adult was on 2 October and the latest sighting on 15 December. The ratio of crabeater pups to adults increased rapidly during the 10-day period 16-25 October, implying a pulse of births over this time. Ross seal pups with an accompanying adult were sighted between 24 October and 22 November, with a peak in the pup-adult ratio occurring in the period 6-15 November. Leopard seal pups were sighted between 8 November and 25 December, with the pup-adult ratio relatively constant during this period. The data provide circumstantial evidence that the maximum durations of lactation reported in the literature for the three species may be over-estimates. If lactation is shorter than reported, asynchrony in the timing of pupping, either among or within years, is implied.

Global Ecology and Biogeography, 2014

Aim Mammalian home range patterns provide information on spatial behaviour and ecological pattern... more Aim Mammalian home range patterns provide information on spatial behaviour and ecological patterns, such as resource use, that is often used by conservation managers in a variety of contexts. However, there has been little research on home range patterns outside of the terrestrial environment, potentially limiting the relevance of current home range models for marine mammals, a group of particular conservation concern. To address this gap, we investigated how variation in mammalian home range size among marine and terrestrial species was related to diet, environment and body mass.

Polar Biology, 2005

This is the first study that has used satellite telemetry to assess the spatial behaviour of adul... more This is the first study that has used satellite telemetry to assess the spatial behaviour of adult leopard seals. Satellite tags on 11 leopard seals transmitted between 29 days and 282 days. Swim speeds, distances swum per day and distances from tagging site were significantly different among individuals and seasons. Swim speeds ranged from 0.004 km/h to 10.86 km/h; distances swum per day from 0 km/day to 150 km/day; and the maximum distances from tagging site ranged from 33.30 km to 319.97 km. Rather than moving northsouth with the ice most seals remained within a 50 km radius of their tagging site from 11 days to 97 days. The relatively sedentary movement of the leopard seals was unexpected, particularly the movement of animals over winter, which although slightly offshore did not reflect the usual northward winter migration described for the leopard seal. But traditionally, the leopard seals' spatial habits have been described from sightings of animals at higher latitudes. These are generally younger animals and their behaviour may not be representative of the adults. This study has focused on adult females and animals at the extreme southerly range of the leopard seal. This highlights the importance of understanding and reporting age structure and distribution when discussing animal spatial behaviour.

PloS one, 2014

Thylacinidae is an extinct family of Australian and New Guinean marsupial carnivores, comprizing ... more Thylacinidae is an extinct family of Australian and New Guinean marsupial carnivores, comprizing 12 known species, the oldest of which are late Oligocene (∼24 Ma) in age. Except for the recently extinct thylacine (Thylacinus cynocephalus), most are known from fragmentary craniodental material only, limiting the scope of biomechanical and ecological studies. However, a particularly well-preserved skull of the fossil species Nimbacinus dicksoni, has been recovered from middle Miocene (∼16-11.6 Ma) deposits in the Riversleigh World Heritage Area, northwestern Queensland. Here, we ask whether N. dicksoni was more similar to its recently extinct relative or to several large living marsupials in a key aspect of feeding ecology, i.e., was N. dicksoni a relatively small or large prey specialist. To address this question we have digitally reconstructed its skull and applied three-dimensional Finite Element Analysis to compare its mechanical performance with that of three extant marsupial carnivores and T. cynocephalus. Under loadings adjusted for differences in size that simulated forces generated by both jaw closing musculature and struggling prey, we found that stress distributions and magnitudes in the skull of N. dicksoni were more similar to those of the living spotted-tailed quoll (Dasyurus maculatus) than to its recently extinct relative. Considering the Finite Element Analysis results and dental morphology, we predict that N. dicksoni likely occupied a broadly similar ecological niche to that of D. maculatus, and was likely capable of hunting vertebrate prey that may have exceeded its own body mass.

Extinction risk varies across species and is influenced by key ecological parameters, such as die... more Extinction risk varies across species and is influenced by key ecological parameters, such as diet specialization. For predictive conservation science to be effective, we need to understand extinction risk factors that may have implicated recent species extinctions. Diet and feeding behaviour of the large extinct marsupial carnivore Thylacinus cynocephalus or thylacine have long been debated. Improved understanding of the skull's biomechanical performance and its limitations in a comparative context may yield important insights. Here, we use three-dimensional (3D) finite element analysis to assess aspects of biomechanical performance in the skull of T. cynocephalus relative to those of two extant marsupial carnivores with known diets that occurred sympatrically with T. cynocephalus: the Tasmanian devil, Sarcophilus harrisii, and spotted-tailed quoll, Dasyurus maculatus. Together, these three species comprised the large mammalian carnivore guild in Tasmania at the time of European settlement. The bone-cracking S. harrisii produced high bite forces for its size as expected, but the stresses induced were surprisingly high. A higher proportion of cancellous bone in the skull of this osteophage may act to absorb shock but decrease rigidity and hence raise stress. A relatively high bite force and rigid skull characterized D. maculatus, which may allow them to target prey of variable sizes. Compared with S. harrisii and D. maculatus, we found that the skull of T. cynocephalus was least well adapted to withstand forces driven solely by its jaw-closing musculature, as well as to simulations of struggling prey. Our findings suggest that T. cynocephalus likely consumed smaller prey relative to its size, which may have had implications for their survival.

The leopard seal is a top-order predator in the Southern Ocean ecosystem and preys on a wide vari... more The leopard seal is a top-order predator in the Southern Ocean ecosystem and preys on a wide variety of vertebrate species including seals and penguins. We assessed the use of hairs found in leopard seal scats to identify the species of pinniped consumed. A reference collection of hairs was obtained from four potential leopard seal prey species including crabeater, Weddell, Ross, and Southern elephant seals. Discrimination techniques applied to terrestrial mammals did not allow for identification of the seal hairs. Instead, a 2-dimensional (2-D) and 6-dimensional (6-D) analysis technique utilising Mahalanobis distances (D 2) was used. The smallest Mahalanobis distance together with the largest value of p(F) positively identified hairs from each species. The 6-D analysis was more accurate and applied to hairs found in the leopard seal scats. The majority of prey species were identified as crabeater seals, which are a known prey item of the leopard seal.

The passage rate of food through the alimentary tract of three captive, female leopard seals (Hyd... more The passage rate of food through the alimentary tract of three captive, female leopard seals (Hydrurga leptonyx) was assessed. Seals were housed during winter in holding pools with access to water to reduce factors affecting digestion. Three different marker types were used; large and small beads and TiO 2 . Animals were checked hourly, and sample collections continued for 270 h after dosing. Individual differences in transit and mean retention times were observed, possibly reflecting inter-digestive emptying times of the stomach and small intestine. Age differences and activity levels may also have been a factor. Leopard seals displayed extended food transit times similar to terrestrial carnivores instead of other pinnipeds. This result suggests an adaptation of digestive system to cope with the opportunistic diet and range of prey types consumed.

Too close for comfort, 2008

Wildlife Research, 2014

Context. Three dolphin species occur in coastal waters of monsoonal northern Australia: the Austr... more Context. Three dolphin species occur in coastal waters of monsoonal northern Australia: the Australian snubfin (Orcaella heinsohni), humpback (Sousa sp.) and the bottlenose (Tursiops sp.). Their overall population size and trends are poorly known, and their conservation status has been difficult to resolve, but can be expected to deteriorate with likely increased development pressures.

Too close for comfort, 2008

Polar Biology, 2003

Biological Conservation, 2012

Marine Ecology-progress Series, 2005

Proceedings. Biological sciences / The Royal Society, Jan 22, 2014

PLoS ONE, 2014

Data on the timing of pupping by the three species of phocid that breed on the Antarctic pack-ice... more Data on the timing of pupping by the three species of phocid that breed on the Antarctic pack-ice (crabeater, Ross and leopard seals) are limited. Better information would improve our understanding of these species' population and reproductive ecologies, and could facilitate planning and design of population surveys. Observations of the presence or absence of pups with adults during numerous voyages of the Australian National Antarctic Research Expeditions to East Antarctica during spring and early summer months are analysed and presented. The earliest sighting in any year of a crabeater pup accompanied by an adult was on 2 October and the latest sighting on 15 December. The ratio of crabeater pups to adults increased rapidly during the 10-day period 16-25 October, implying a pulse of births over this time. Ross seal pups with an accompanying adult were sighted between 24 October and 22 November, with a peak in the pup-adult ratio occurring in the period 6-15 November. Leopard seal pups were sighted between 8 November and 25 December, with the pup-adult ratio relatively constant during this period. The data provide circumstantial evidence that the maximum durations of lactation reported in the literature for the three species may be over-estimates. If lactation is shorter than reported, asynchrony in the timing of pupping, either among or within years, is implied.

Global Ecology and Biogeography, 2014

Polar Biology, 2005

PloS one, 2014

Too close for comfort, 2008

Wildlife Research, 2014

Too close for comfort, 2008

We examined recordings from a 15-month (May 2009–July 2010) continuous acoustic data set collecte... more We examined recordings from a 15-month (May 2009–July 2010) continuous acoustic data set collected from a bottom-mounted passive acoustic recorder at a sample frequency of 6kHz off Portland, Victoria, Australia (38°33′01″S, 141°15′13″E) off southern Australia. Analysis revealed that calls from both subspecies were recorded at this site, and general additive modeling revealed that the number of calls varied significantly across seasons. Antarctic blue whales were detected more frequently from July to October 2009 and June to July 2010, corresponding to the suspected breeding season, while Australian blue whales were recorded more frequently from March to June 2010, coinciding with the feeding season. In both subspecies, the number of calls varied with time of day; Antarctic blue whale calls were more prevalent in the night to early morning, while Australian blue whale calls were detected more often from midday to early evening. Using passive acoustic monitoring, we show that each subspecies adopts different seasonal and daily call patterns which may be related to the ecological strategies of these subspecies. This study demonstrates the importance of passive acoustics in enabling us to understand and monitor subtle differences in the behavior and ecology of cryptic sympatric marine mammals.

Climate-induced changes may be more substantial within the marine environment, where following ec... more Climate-induced changes may be more substantial within the marine environment, where following ecological change is logistically difficult, and typically expensive. As marine animals tend to produce stereotyped, long-range signals, they are ideal for repeatable surveying. In this study we illustrate the potential for calling rates to be used as a tool for determining habitat quality by using an Antarctic pack-ice seal, the leopard seal, as a model.With an understanding of the vocal behavior of a species, their seasonal and diurnal patterns, sex and age-related differences, an underwater passive-acoustic survey conducted alongside a visual survey in an arc of 4,225 km across the Davis Sea, Eastern Antarctica, showed that while acoustic and visual surveys identified similar regions as having high densities, the acoustic surveys surprisingly identified the opposite regions as being ‘critical’ habitats. Density surveys of species that cannot be differentiated into population classes may be misleading because overall density can be a negative indicator of habitat quality.Under special circumstances acoustics can offer enormous advantage over traditional techniques and open up monitoring to regions that are remote, difficult and expensive to work within, no longer restricting long-term community assessment to resource-wealthy communities. As climatic change affects a broad range of organisms across geographic boundaries we propose that capitalizing on the significant advances in passive acoustic technology, alongside physical acoustics and population modeling, can help in addressing ecological questions more broadly.

Leopard seals (Hydrurga leptonyx) are top predators in the Antarctic ecosystem. They produce ster... more Leopard seals (Hydrurga leptonyx) are top predators in the Antarctic ecosystem. They produce stereotyped calls as part of a stylized underwater vocal display. Understanding of their acoustic behavior is improved by identifying the amplitude of their calls. The amplitude of five types of calls (n ¼ 50) from a single male seal were measured as broadband source levels and ranged from 153 to 177 dB re 1 lPa at 1 m. The mean source levels differed between call types, the lower frequency calls (L, D, and O) tended to have source levels 10 dB higher than the higher frequency calls (H and M). Information on call-type source levels is important to take into account for passive acoustic studies investigating repertoire usage as calls produced with greater amplitudes are likely to have larger acoustic ranges, especially when these are also the calls with lower frequencies, such as is the case in leopard seals.

Aquatic Mammals, 2005

Phocid life history and vocal repertoire size data gathered from the literature were examined wit... more Phocid life history and vocal repertoire size data gathered from the literature were examined with independent contrasts analyses to assess whether there is a significant relationship between sexual selection and vocal repertoire size. Investigations showed that the degree of polygyny does not influence vocal repertoire size of males, but was strongly influenced by the strategy of maternal care adopted by females. Species where females remain with their pups while nursing ("attending females") have males with simple crude vocal repertoires used in male-male agonistic interactions. In these species, male elephant (Mirounga sp.), grey (Halichoerus grypus), crabeater (Lobodon carcinophagus), and hooded (Cystophora cristata) seals generally have greater access to estrus females while they are still hauled out ashore. In species where females continue to go to sea while raising their pups ("foraging females"), males have broader advertising vocal repertoires. The stability of the haul-out platform during breeding used by the females makes a further impact, however. Where "foraging-females" breed in unstable pack ice, males have little chance of predictably locating routes used by estrus females while traveling to and from feeding grounds. These species, the leopard (Hydrurga leptonyx), Ross (Ommatophoca rossii), bearded (Erignathus barbatus), and ribbon (Histriophoca fasciata) seals, have intermediate- sized repertoires used in long-range underwater acoustic displays (scattergun advertising). The third group, the Weddell (Leptonychotes weddellii), harp (Pagophilus groenlandicus), harbour (Phoca vitulina), and ringed (Pusa hispida) seals, have the largest vocal repertoires. In these species, "foraging-females" breed in stable environments, so males perform underwater acoustic advertisement displays (local advertising) in the vicinity of predictable feeding routes used by estrus females. Because these signals are not constrained by propagation, a large array of sound types have developed.

Abstract: A series of natural history factors were examined to identify which are likely to influ... more Abstract: A series of natural history factors were examined to identify which are likely to influence acoustic behaviour in male phocid seals. Contrary to traditional thought, the degree of polygyny did not appear to influence vocal repertoire size or the other acoustic features examined. However, degree of sexual dimorphism, stability of the pupping substrate and density, guard-ability and predictability of oestrus females, and function of the signals, all appear to be important. Species pupping in stable habitats tend to have vocalizations which are low in minimum frequency, whereas pack-ice breeders have vocalizations with high minimum frequencies. In species where oestrus females are predictably distributed and guardable (the southern elephant, Mirounga leonina, northern elephant, Mirounga angustirostris, grey, Halichoerus grypus, hooded, Cystophora cristata, and crabeater, Lobodon carcinophagus, seals) the acoustic displays of the males tend to be associated with male-male agonistic interactions and are likely to be intrasexual in function. Male vocal repertoires tend to be simple in form composed of a reduced number of primarily broadband pulsed sounds following Morton's (1982) Motivational Structural Hypothesis. However, in species where females do not remain hauled-out with their pups until weaning it is more difficult for males to physically guard them until oestrus. If oestrus females are inaccessible to males, either because they are moving to and from the sea or because they are widely distributed, males could use vocal displays to attract a mate. When oestrus females are widely and unpredictably dispersed long-range underwater advertisement displays are necessary (Scattergun advertizing). The acoustic displays of males of these species (leopard, Hydrurga leptonyx ; Ross, Ommatophoca rossii; bearded, Erignathus barbatus; and ribbon, Histriophoca fasciata, seals) must travel long distances. Sounds that are required to travel over long distances could change slightly in character due to the differing propagation characteristics of the varying frequency components within the vocalization. The signal also could be masked by background noise. Perhaps it is easier for a listening seal to recognize a smaller number of stereotyped vocalizations. Therefore, these seals tend to have fewer, narrowband, highly stereotyped sounds used in stylized repetitive displays which helps ensure that the signal is recognized by a receiving seal at a distance. In species where oestrus females are predictably distributed, but unguarded (Weddell, Leptonychotes weddellii; harp, Pagophilus groenlandicus; harbour, Phoca vitulina; and ringed, Phoca hispida seals) males perform shorter-range underwater advertisement displays. The signals of species advertizing to a local audience are not constrained by propagation difficulties. These species therefore adopt a large array of sound types, and include subtle variations of the same sound type, greatly increasing their overall repertoire size (Local advertizing).

The Journal of the Acoustical Society of America, 2007

During the breeding season, the underwater vocalizations and calling rates of adult male leopard ... more During the breeding season, the underwater vocalizations and calling rates of adult male leopard seals are highly stereotyped. In contrast, sub-adult males have more variable acoustic behavior. Although adult males produce only five stereotyped broadcast calls as part of their long-range underwater breeding displays the sub-adults have a greater repertoire including the adult-like broadcast calls, as well as variants of these. Whether this extended repertoire has a social function is unknown due to the paucity of behavioral data for this species. The broadcast calls of the sub-adults are less stereotyped in their acoustic characteristics and they have a more variable calling rate. These age-related differences have major implications for geographic variation studies, where the acoustic behavior of different populations are compared, as well as for acoustic surveying studies, where numbers of calls are used to indicate numbers of individuals present. Sampling regimes which unknowingly include recordings from sub-adult animals will artificially exaggerate differences between populations and numbers of calling animals. The acoustic behavior of sub-adult and adult male leopard seals were significantly different and although this study does not show evidence that these differences reflect vocal learning in the male leopard seal it does suggest that contextual learning may be present.

Toneburst-evoked auditory brainstem responses (ABRs) were recorded in a captive subadult male leo... more Toneburst-evoked auditory brainstem responses (ABRs) were recorded in a captive subadult male leopard seal. Three frequencies from 1 to 4 kHz were tested at sound levels from 68 to 122 dB peak equivalent sound pressure level (peSPL). Results illustrate brainstem activity within the 1–4 kHz range, with better hearing sensitivity at 4 kHz. As is seen in human ABR, only wave V is reliably identified at the lower stimulus intensities. Wave V is present down to levels of 82 dB peSPL in the right ear and 92 dB peSPL in the left ear at 4 kHz. Further investigations testing a wider frequency range on seals of various sex and age classes are required to conclusively report on the hearing range and sensitivity in this species.

Vocalisations and vocalising bouts of adult male leopard seals recorded from the Prydz Bay region... more Vocalisations and vocalising bouts of adult male leopard seals recorded from the Prydz Bay region, East Antarctica, were compared to determine whether they showed individual variability. There were distinct individual patterns in the sequence of vocalisations within vocalising bouts. A sequence could be reliably ascribed to a particular individual with a high degree (83%) of certainty. Such sequences may carry information about the identity of the caller. Acoustic characteristics of the two most commonly used vocalisations, the high and low double trills, showed weak within individual variation. Although differences were observed among individuals in the high double trill few were observed in the low double trill consequently the low double trills of some individuals could not be reliably ascribed to any particular seal.

Behavioural Processes, 2008

Many territorial species have the ability to recognise neighbours from stranger individuals. If t... more Many territorial species have the ability to recognise neighbours from stranger individuals. If the neighbouring individual is assumed to pose less of a threat, the territorial individual responds less and avoids unnecessary confrontations with familiar individuals at established boundaries, thus avoiding the costly energy expenditure associated with fighting. Territorial male Australian fur seals respond more to strangers than to neighbouring males. The present study evaluated which acoustic features were important in the neighbour–stranger recognition process in male Australian fur seals. The results reveal that there was an increase in response strength or intensity from males when they heard more bark units, indicating the importance of repetition to detect a caller. However, lengthening and shortening the inter-unit spaces, (i.e. changing the rhythm of the call) did not appear to significantly affect an animal's response. In addition, the whole frequency spectrum was considered important to recognition with results suggesting that they may vary in their importance. A call containing the dominant and surrounding harmonics was considered important to a male's ability to recognise its neighbour. Furthermore, recognition occurs even with a partial bark, but males need to hear between 25 and 75% of each bark unit from neighbouring seals. Our study highlights which acoustic features induce stronger or weaker responses from territorial males, decoding the important features in neighbour–stranger recognition.

Bioacoustics, 2005

Australian fur seals Arctocephalus pusillus doriferus are colonial breeding animals forming dense... more Australian fur seals Arctocephalus pusillus doriferus are colonial breeding animals forming dense social groups during the breeding season. During this time, males establish and defend territories through physical conflicts, stereotyped posturing and vocalisations. While vocalisations are suggested to play an important role in male recognition systems, it has received little attention. Recordings of nine adult male Australian fur seals were made during the 2000 and 2001 breeding seasons at Kanowna Island (39° 10′S, 146° 18′ E), Bass Strait, Australia. The in-air bark vocalisations of territory-holding males were used to characterise the Bark Call and to determine whether males produce individually distinct calls, which could be used as a basis for vocal recognition. Seventeen frequency and temporal variables were measured from a total of 162 barks from nine individual males. The Bark Series was more reliably classified (83%) to the correct caller compared to the Bark Unit. This was assigned with less certainty (68%), although the classification was still relatively high. Findings from this study indicate that there is sufficient stereotypy within individual calls, and sufficient variation between them, to enable vocal recognition in male Australian fur seals.

The Journal of the Acoustical Society of America, 2006

Otariid seals (fur seals and sea lions) are colonial breeders with large numbers of females givin... more Otariid seals (fur seals and sea lions) are colonial breeders with large numbers of females giving birth on land during a synchronous breeding period. Once pups are born, females alternate between feeding their young ashore and foraging at sea. Upon return, both mother and pup must relocate each other and it is thought to be primarily facilitated by vocal recognition. Vocalizations of thirteen female Australian fur seals (Arctocephalus pusillus doriferus) were recorded during the breeding seasons of December 2000 and 2001, when pups are aged from newborns to one month. The pup attraction call was examined to determine whether females produce individually distinct calls which could be used by pups as a basis for vocal recognition. Potential for individual coding, discriminant function analysis (DFA), and classification and regression tree analysis were used to determine which call features were important in separating individuals. Using the results from all three analyses:F0, MIN F and DUR were considered important in separating individuals. In 76% of cases, the PAC was classified to the correct caller, using DFA, suggesting that there is sufficient stereotypy within individual calls, and sufficient variation between them, to enable vocal recognition by pups of this species.

Marine mammal …, 2008

The vocal repertoire, structure, and behavioral context of airborne vocalizations produced by Aus... more The vocal repertoire, structure, and behavioral context of airborne vocalizations produced by Australian fur seals (Arctocephalus pusillus doriferus) are described using recordings made at a breeding colony on Kanowna Island, Bass Strait, Australia. The study identified six different call types: three produced by males (bark, guttural threat, and submissive call); five produced by females (bark, guttural threat, submissive call, growl, and pup attraction call) and the female attraction call produced by pups and yearlings. Vocalizations were compared according to age and sex classes. The overall structure and function of the pup attraction and female attraction call produced by females, yearlings, and pups, was similar. However, while similar in their overall appearance, certain call types have a lower fundamental frequency when compared with other fur seals. In addition, the male bark call alters in rate of production according to the context used, where calls are slower when males are stationary and advertising their territorial status and faster when males are involved in confrontations with other males or actively herding females. Further research is required to investigate changes in environmental conditions and their effects on shaping the call structure and communication in Australian fur seals.

Marine Mammal Science, 2008

Australian Mammalogy, 2009

Seasonal changes in reproductive and acoustic behaviour are potentially affected by hormonal fluc... more Seasonal changes in reproductive and acoustic behaviour are potentially affected by hormonal fluctuations; however, as it is difficult to routinely sample marine mammals, these associations are mostly inferred. Australian fur seals are vocal marine mammals that have a highly synchronous breeding season. The present study collected information on the testosterone concentration in faeces, vocalisations and behaviour of two captive male Australian fur seals to determine whether there are any associations between these variables. Positive associations were evident between the non-interactive agonistic behaviours (Head sway, Lay down and Head up) and an increase in calling rate of the bark calls in males. Barks were highest during August through to October, corresponding to the breeding period, while faecal testosterone levels peaked in September, coinciding with the high frequency in the calling rates of barks. Guttural threat calls were rarely heard throughout the year, but peaked in August. This call was not frequently heard but was associated with specific behaviours that were produced during more intense fighting interactions. This study presents preliminary information on the vocalisations, behaviour and hormone profiles for two captive Australian fur seals. Future studies with increased sample sizes from both wild and captive animals would clarify the intricate association between these factors.

Marine Mammal Science, 2006

As a result of selective pressures faced during lactation, vocal recognition may play a crucial r... more As a result of selective pressures faced during lactation, vocal recognition may play a crucial role in maintaining the phocid mother–pup bond during the period of dependence. To investigate this possibility, we examined whether Weddell seal (Leptonychotes weddellii) pups produce individually distinctive “primary” calls. One temporal, nine fundamental frequency features, and two spectral characteristics were measured. A discriminant function analysis (DFA) of 15 Vestfold Hills pups correctly classified 52% of calls, while the cross-validation procedure classified 29% of calls to the correct pup. A second DFA of 10 known-age McMurdo Sound pups correctly classified 44% of “test” calls. For novel calls, the probabilities of attaining such classification rates by chance are low. The relationship between age and call stereotypy indicated that pups 2 wk and older may be more vocally distinctive. Overall, findings suggest that Weddell seal pup “primary” calls are moderately distinctive and only exhibit sufficient stereotypy to aid maternal recognition by approximately two weeks of age.

The Journal of the Acoustical Society of America, 2005

... Tracey L. Rogers, Gayle A. Rowney, Michaela B. Ciaglia, Douglas H. Cato. ... and 10 January 2... more ... Tracey L. Rogers, Gayle A. Rowney, Michaela B. Ciaglia, Douglas H. Cato. ... and 10 January 2004 off Mawson, Eastern Antarctica (660 44.243S and 690 48.748E). Recordings were made using an Acoustics Recording Package (ARP by Dr. John Hildebrand, Scripps Institute of ...

Encyclopedia of Marine Mammals, 2009

Marine Mammal Science, 2002

We immobilized 200-550-kg leopard seals (Hydrurga leptonyx) on sea ice in Prydz Bay, Antarctica (... more We immobilized 200-550-kg leopard seals (Hydrurga leptonyx) on sea ice in Prydz Bay, Antarctica (68"25'S, 77'10'E) between November 1997 and February 2000. Midazolam (0.18-0.27 mgikgfi pethidine (1 .O-1.5 mgikg) was administered by dart to 16 leopard seals. Unpredictable immobilization, poor airway maintenance, and our inability to fully assess the suitability of flumazenil (0.003-0.01 mg/kg), naloxone (0.01-0.013 mgikg), and naltrexone (0.05-0.12 mgikg) as reversal agents limited suitability of midazolam/ pethidine. Tiletamineizolazepam 1:l (0.5-1.5 rng/kg) was, therefore, adrninistered to 19 leopard seals. It produced faster induction (19 ? 3 min), more effective and reliable response to dose (rank correlation: r,r = 0.88, n = 18), and better pulmonary ventilation and faster return of cognitive function upon recovery, in comparison to midazolam/pethidine. Best results were achieved with tiletamineizolazepam (1.2-1.4 mgikg) which safely immobilized seven of nine seals for 20-30 min. Entry to the water upon darting was minimized, but not eliminated, by the use of lightweight air-pressurized darts and a thorough knowledge of leopard seal behavior.

Journal of Wildlife Management, 2005

Leopard seals (Hydrurga leptonyx) are formidable marine predators and require sedation before sci... more Leopard seals (Hydrurga leptonyx) are formidable marine predators and require sedation before scientific examination. Mass-specific drug dosage for leopard seals has usually been determined from generic allometric equations or visual estimates. However, the leopard seal is a slender phocid and generic equations are likely to return inaccurate mass estimates, which may lead to fatal overdoses of drugs. We used published and unpublished morphometric data to construct allometric models for estimating leopard seal body mass. The model using volume (Vol), which combined measures of snout-tail length (STL) and the square of girth (G 2 ), provided our best estimate of mass (r 2 = 0.97). The model using STL alone was sample-site specific (each r 2 ≥ 0.85), highlighting G as an important measure to obtain where possible. The confidence and prediction intervals associated with each model broadened with increased seal size and decreased sample size, suggesting the use of extra caution when estimating drug dosage for larger seals to avoid over-or under-dosing. We also developed a seal body condition index that can assist wildlife management when deciding if rehabilitation of vagrant seals is warranted. Body condition may also affect the induction, duration and recovery times of anaesthetized leopard seals.

Polar Biology, 2009

... T. Rogers Á M. Ciaglia Evolution and Ecology Research Centre, School of BEES, University of N... more ... T. Rogers Á M. Ciaglia Evolution and Ecology Research Centre, School of BEES, University of New South Wales, Sydney, NSW, Australia 123 ... that which was observed twice or more as harem bull in any harem throughout the breeding period, while the subordi-nate male was ...

Journal of anatomy, 2006

The microscopic anatomy of the cardio-respiratory system, digestive system, kidney, lymphatic sys... more The microscopic anatomy of the cardio-respiratory system, digestive system, kidney, lymphatic system and integument was investigated in the leopard seal, Hydrurga leptonyx , by examining histological sections of tissues collected from leopard seals in Antarctica and New South Wales, Australia. The majority of the tissues had similar histological features to those described in terrestrial mammals and other pinniped species, particularly phocid seals. Differences noted included readily identifiable Purkinje cells within the endocardium, muscular rather than cartilaginous reinforcement of the smaller airways, a single capillary layer within the alveolar septa, limited and variable keratinization of the oesophageal epithelium, few lymphoid follicles within the lamina propria of the gastrointestinal tract, and an absence of a sporta perimedullaris musculosa described in the kidney of cetaceans and some pinniped species. Adaptations of the lung, spleen and integument, similar to those described in other pinnipeds, including reinforcement of the pulmonary terminal airways, prominent pulmonary interlobular septa, ample smooth muscle in the capsule and trabeculae of the spleen, increased thickness of the epidermis, welldeveloped dermal sebaceous glands, and a thick blubber layer, appear to confer upon the leopard seal advantages related to its aquatic lifestyle.

Comparative Biochemistry and Physiology B-biochemistry & Molecular Biology, 2005

Blood protein analysis including total serum protein and albumin by chemical methods, fibrinogen ... more Blood protein analysis including total serum protein and albumin by chemical methods, fibrinogen estimation and serum protein electrophoresis (SPE) was performed on the leopard seal, Hydrurga leptonyx. The most commonly observed SPE pattern was eight fractions designated albumin, α1a, α1b, α2a, α2b, β1, β2 and γ-globulin. Significantly higher total serum protein and albumin concentrations, as determined by chemical methods, and significantly higher α2-globulin concentrations, determined by SPE, were seen in free-ranging male seals compared to females, whilst significantly higher β-globulin concentrations were seen in female seals. Season of sampling influenced fibrinogen and β2-globulin concentrations, whereas there were no significant differences in any protein concentrations with moult status. Qualitative comparison of SPE traces of leopard seals in Antarctica with “sick” individuals in NSW, Australia revealed obvious differences, as did quantitative comparison of protein concentrations where differences in α1, α2, β1, β2, and γ-globulin concentrations were seen. These findings suggest that SPE is a useful tool for investigating serum proteins in the leopard seal, with applications for the investigation of “sick” individuals and the assessment of variation in homeostasis. This technique could also be used to identify the presence of environmental stressors, subclinical disease and physiological variation within specific seal populations.

Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 2004

Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology, 2005

Blood protein analysis including total serum protein and albumin by chemical methods, fibrinogen ... more Blood protein analysis including total serum protein and albumin by chemical methods, fibrinogen estimation and serum protein electrophoresis (SPE) was performed on the leopard seal, Hydrurga leptonyx. The most commonly observed SPE pattern was eight fractions designated albumin, a 1a , a 1b , a 2a , a 2b , h 1 , h 2 and g-globulin. Significantly higher total serum protein and albumin concentrations, as determined by chemical methods, and significantly higher a 2 -globulin concentrations, determined by SPE, were seen in free-ranging male seals compared to females, whilst significantly higher h-globulin concentrations were seen in female seals. Season of sampling influenced fibrinogen and h 2 -globulin concentrations, whereas there were no significant differences in any protein concentrations with moult status. Qualitative comparison of SPE traces of leopard seals in Antarctica with ''sick'' individuals in NSW, Australia revealed obvious differences, as did quantitative comparison of protein concentrations where differences in a 1 , a 2 , h 1 , h 2 , and g-globulin concentrations were seen. These findings suggest that SPE is a useful tool for investigating serum proteins in the leopard seal, with applications for the investigation of ''sick'' individuals and the assessment of variation in homeostasis. This technique could also be used to identify the presence of environmental stressors, subclinical disease and physiological variation within specific seal populations. D

Health of Antarctic Wildlife, 2009

Science of The Total Environment, 2008

Leopard seal, Hydrurga leptonyx, and Weddell seal, Leptonychotes weddellii, occupy an upper troph... more Leopard seal, Hydrurga leptonyx, and Weddell seal, Leptonychotes weddellii, occupy an upper trophic level within the Antarctic ecosystem and are useful indicator species in the Southern Ocean of trace element concentrations. Reference values for the concentration of 19 trace elements were determined in the serum and hair of leopard and Weddell seals sampled in Eastern Antarctica. These reference values can be used as 'baseline' levels for monitoring trace element concentrations in these species. Greater trace element concentrations were determined in hair compared to serum, indicating different time scales of trace element accumulation in these samples. For the majority of trace elements, except for Se in the leopard seal samples and Cr in the Weddell seal samples, significant regression relationships for trace element concentrations in hair and serum were not elucidated. Significant differences were determined in the concentrations of seven out of 15 elements with hair type, moult and new, in the leopard seal; concentrations in moult hair

Zoo Biology, 2006

This study investigated the feasibility and validity of using non-invasively collected ice urine ... more This study investigated the feasibility and validity of using non-invasively collected ice urine samples to measure cortisol concentrations in Weddell seals. Radio-immunoassays were used to determine urinary cortisol, and spectrophotometric assay was used to determine creatinine concentrations. This allowed for urinary cortisol/creatinine ratios (UCCR) to be compared between pure urine and urine collected from the ice. Urinary cortisol/creatinine ratios values of ice urine proved an effective method of studying cortisol concentrations in Weddell seals as there was no difference between pure urine and ice urine UCCR values. There were no inter-sexual or age-related differences in UCCR values in either pure or ice urine. Zoo Biol 0:1–8, 2006. © 2006 Wiley-Liss, Inc.

PloS one, 2013

After birth, mammals acquire a community of bacteria in their gastro-intestinal tract, which harv... more After birth, mammals acquire a community of bacteria in their gastro-intestinal tract, which harvests energy and provides nutrients for the host. Comparative studies of numerous terrestrial mammal hosts have identified host phylogeny, diet and gut morphology as primary drivers of the gut bacterial community composition. To date, marine mammals have been excluded from these comparative studies, yet they represent distinct examples of evolutionary history, diet and lifestyle traits. To provide an updated understanding of the gut bacterial community of mammals, we compared bacterial 16S rRNA gene sequence data generated from faecal material of 151 marine and terrestrial mammal hosts. This included 42 hosts from a marine habitat. When compared to terrestrial mammals, marine mammals clustered separately and displayed a significantly greater average relative abundance of the phylum Fusobacteria. The marine carnivores (Antarctic and Arctic seals) and the marine herbivore (dugong) possessed significantly richer gut bacterial community than terrestrial carnivores and terrestrial herbivores, respectively. This suggests that evolutionary history and dietary items specific to the marine environment may have resulted in a gut bacterial community distinct to that identified in terrestrial mammals. Finally we hypothesize that reduced marine trophic webs, whereby marine carnivores (and herbivores) feed directly on lower trophic levels, may expose this group to high levels of secondary metabolites and influence gut microbial community richness.

Environmental Microbiology, 2013

The gut microbiota of mammals underpins the metabolic capacity and health of the host. Our unders... more The gut microbiota of mammals underpins the metabolic capacity and health of the host. Our understanding of what influences the composition of this community has been limited primarily to evidence from captive and terrestrial mammals. Therefore, the gut microbiota of southern elephant seals, Mirounga leonina, and leopard seals, Hydrurga leptonyx, inhabiting Antarctica were compared with captive leopard seals. Each seal exhibited a gut microbiota dominated by four phyla: Firmicutes (41.5 Ϯ 4.0%), Fusobacteria (25.6 Ϯ 3.9%), Proteobacteria (17.0 Ϯ 3.2%) and Bacteroidetes (14.1 Ϯ 1.7%). Species, age, sex and captivity were strong drivers of the composition of the gut microbiota, which can be attributed to differences in diet, gut length and physiology and social interactions. Differences in particular prey items consumed by seal species could contribute to the observed differences in the gut microbiota. The longer gut of the southern elephant seal provides a habitat reduced in available oxygen and more suitable to members of the phyla Bacteroidetes compared with other hosts. Among wild seals, 16 'core' bacterial community members were present in the gut of at least 50% of individuals. As identified between southern elephant seal mother-pup pairs, 'core' members are passed on via vertical transmission from a young age and persist through to adulthood. Our study suggests that these hosts have co-evolved with their gut microbiota and core members may provide some benefit to the host, such as developing the immune system. Further evidence of their strong evolutionary history is provided with the presence of 18 shared 'core' members in the gut microbiota of related seals living in the Arctic. The influence of diet and other factors, particularly in captivity, influences the composition of the community considerably. This study suggests that the gut microbiota has co-evolved with wild mammals as is evident in the shared presence of 'core' members.

We demonstrate that the exhaled breath condensate, or 'blow', from marine mammals can be used to ... more We demonstrate that the exhaled breath condensate, or 'blow', from marine mammals can be used to examine respiratory associated microbial communities using non-invasive sampling methods. Blow samples from two species of bottlenose dolphin, Tursiops truncatus and T. aduncus, along with hybrid offspring, were examined using molecular microbial ecology methods. A temporal analysis revealed that microbial community structure of each individual remained distinct from other individuals over a twomonth period, indicting strong host specificity. The taxonomic composition of samples, based on pyrosequencing of the V1-V3 regions of the 16S rRNA gene, from 24 healthy individuals was dominated by the Cardiobacteraceae lineage of Gammaproteobacteria, comprising on average 52% of sequences in all samples. Sequences in this taxa were associated with novel clades that contain only sequences from dolphin respiratory tracts. Other genera that likely form part of the core biota include the Saccharospirillaceae (Gammaproteobacteria),

Little penguins, Eudyptula minor, were once common along the Sydney coastline; however, today alm... more Little penguins, Eudyptula minor, were once common along the Sydney coastline; however, today almost all breeding penguins in the region are found on a small island in the mouth of the Hawkesbury River. During a four-year study, the reproductive success of breeding birds on Lion Island was higher and less variable than that reported from other areas. The early commencement of breeding, and the high and stable breeding success during the study suggested that the colony had access to an abundant and stable food source. In addition, success was not reduced by introduced predators and human disturbance is relatively low. However, continued monitoring will be required to gain accurate information on the long-term viability of this colony as penguin breeding success is known to fluctuate widely between years.

Wildlife Research, 2014

Marine Mammal Science, 2006

As a result of selective pressures faced during lactation, vocal recognition may play a crucial r... more As a result of selective pressures faced during lactation, vocal recognition may play a crucial role in maintaining the phocid mother-pup bond during the period of dependence. To investigate this possibility, we examined whether Weddell seal (Leptonychotes weddellii) pups produce individually distinctive "primary" calls. One temporal, nine fundamental frequency features, and two spectral characteristics were measured. A discriminant function analysis (DFA) of 15 Vestfold Hills pups 933 934 MARINE MAMMAL SCIENCE, VOL. 22, NO. 4, 2006 correctly classified 52% of calls, while the cross-validation procedure classified 29% of calls to the correct pup. A second DFA of 10 known-age McMurdo Sound pups correctly classified 44% of "test" calls. For novel calls, the probabilities of attaining such classification rates by chance are low. The relationship between age and call stereotypy indicated that pups 2 wk and older may be more vocally distinctive. Overall, findings suggest that Weddell seal pup "primary" calls are moderately distinctive and only exhibit sufficient stereotypy to aid maternal recognition by approximately two weeks of age.

Microbiology Australia, 2015

Environmental Microbiology, 2013

Journal of Wildlife Management, 2005

… journal of animal sound and its …, Jan 1, 2011

Toneburst-evoked auditory brainstem responses (ABRs) were recorded in a captive subadult male leo... more Toneburst-evoked auditory brainstem responses (ABRs) were recorded in a captive subadult male
leopard seal. Three frequencies from 1 to 4 kHz were tested at sound levels from 68 to 122 dB peak
equivalent sound pressure level (peSPL). Results illustrate brainstem activity within the 1–4 kHz
range, with better hearing sensitivity at 4 kHz. As is seen in human ABR, only wave V is reliably
identified at the lower stimulus intensities. Wave V is present down to levels of 82 dB peSPL in the
right ear and 92 dB peSPL in the left ear at 4 kHz. Further investigations testing a wider frequency
range on seals of various sex and age classes are required to conclusively report on the hearing range
and sensitivity in this species.

Thylacinidae is an extinct family of Australian and New Guinean marsupial carnivores, comprizing ... more Thylacinidae is an extinct family of Australian and New Guinean marsupial carnivores, comprizing 12 known species, the oldest of which are late Oligocene (,24 Ma) in age. Except for the recently extinct thylacine (Thylacinus cynocephalus), most are known from fragmentary craniodental material only, limiting the scope of biomechanical and ecological studies. However, a particularly well-preserved skull of the fossil species Nimbacinus dicksoni, has been recovered from middle Miocene (,16-11.6 Ma) deposits in the Riversleigh World Heritage Area, northwestern Queensland. Here, we ask whether N. dicksoni was more similar to its recently extinct relative or to several large living marsupials in a key aspect of feeding ecology, i.e., was N. dicksoni a relatively small or large prey specialist. To address this question we have digitally reconstructed its skull and applied three-dimensional Finite Element Analysis to compare its mechanical performance with that of three extant marsupial carnivores and T. cynocephalus. Under loadings adjusted for differences in size that simulated forces generated by both jaw closing musculature and struggling prey, we found that stress distributions and magnitudes in the skull of N. dicksoni were more similar to those of the living spotted-tailed quoll (Dasyurus maculatus) than to its recently extinct relative. Considering the Finite Element Analysis results and dental morphology, we predict that N. dicksoni likely occupied a broadly similar ecological niche to that of D. maculatus, and was likely capable of hunting vertebrate prey that may have exceeded its own body mass.

Journal of Mammalogy, 2015

For effective species management, understanding population structure and distribution is critical... more For effective species management, understanding population structure and distribution is critical. However, quantifying population structure is not always straightforward. Within the Southern Hemisphere, the blue whale (Balaenoptera musculus) complex is extremely diverse but difficult to study. Using automated detector methods, we identified "acoustic populations" of whales producing region-specific call types. We examined blue whale call types in passive acoustic data at sites spanning over 7,370 km across the southeast Indian Ocean and southwest Pacific Ocean (SWPO) from 2009 to 2012. In the absence of genetic resolution, these acoustic populations offer unique information about the blue whale population complex. We found that the Australian continent acts as a geographic boundary, separating Australia and New Zealand blue whale acoustic populations at the junction of the Indian and Pacific Ocean basins. We located blue whales in previously undocumented locations, including the far SWPO, in the Tasman Sea off the east coast of Australia, and along the Lau Basin near Tonga. Our understanding of population dynamics across this broad scale has significant implications to recovery and conservation management for this endangered species, at a regional and global scale.